Too numerous to list individually. Please read the review.

Suzuki Factory Service Repair Manual PDF1.

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This subject of this review is the La Cimbali M21, Junior DT/1 “Casa.” In other words, La Cimbali’s latest, automatic single group, with pre-infusion, dual pressure gauge, and “improved” steam tip. It is not about any of the other La Cimbali Juniors, other than in passing.
Note that the improvements came about after consultation between Chris Nachtrieb of Chris Coffee and La Cimbali. It’s to their mutual credit that he insisted and they listened and executed.
Before reading this review, read everything you can find which Ken Fox wrote about either of his Juniors, and Dan Kehn’s review on the pre-Casa (M21) Junior DT/1 posted in the review section of Home-Barista. Their authors are especially knowledgeable and provide a lot of information which is true about all Juniors, as well as context by discussing older models. It’s a good idea to read all the reviews here on CoffeeGeek as I’ll address some of the points raised there.
I intended to review this machine here and on my blog since buying one more than eight months ago. One thing and another has kept me from posting much of anything anywhere, but my reaction to the Casa was a special and powerful inducement for procrastination. It was hard for me to find enough wrong with it to write credibly. I find it hard to believe “all 10s,” even my own. But what are you gonna do? One calls 'em like one sees 'em, don't one?
Perhaps the largest difference between the new Casa and earlier models of the Junior DT/1, is pre-infusion. You have the option of starting the pump (which ramps up very quickly) or four seconds of line pressure pre-infusion. Pre-infusion is selected when the user presses and holds any of the four volumetric buttons for more than two seconds. The other differences are a new pressure gauge which shows both boiler and pump pressure (nice, I guess); and a modified steam tip (at least if you buy it from Chris), which is a little slower than the old tip -- about 15 seconds to froth 7 oz of milk, and far more home-barista friendly.
Enough with the preamble already.
Make no mistake about it, the Casa is not 'prosumer,' it's a true commercial design which really works in the home. It's very consistent; has unmatchable ergonomics; beautiful to look at; a pleasure to touch; easy to clean; everything functions; there's plenty of mass in the direct connection between boiler and group; no gimmicks; no construction shortcuts; top quality components (although every p-stat has its deficiencies and detractors); etc., ad damn near infinitum. It's conservatively designed, well-engineered and more “cost is no object,” than built to a particular price point. The Casa is about as good as a heat exchanger (HX) espresso machine gets.
I think most people interested in a machine of this caliber and price have already limited their choices down to a few, with the first threshold decision being the decision between a double-boiler, PID (DBPID) controlled machine and an HX. Given that DBPIDs really do work, is there still a place for an HX?
Yes. DBPIDs really do work but mostly in the sense of reassurance. They don’t actually make better coffee than a well-made, well operated HX.
Although requiring attention and a modicum of judgment, the techniques of controlling HX temperatures are not particularly difficult. Because of its easily interpreted sounds, “dosometric” water controls, and fast rebound to whatever base temperature is imposed by the p-stat setting, the Junior can be controlled with enough precision to make consistently good coffee.
Perhaps now is a good time to mention that the dual manometer makes set up somewhat easier than with the old single needle job – but only somewhat. You don’t use the gauge very often. Or at least I don’t.
In practice, that means pulling a 'cooling shot' through a clean pf. The size of the cooling shot depends on how long the machine has idled; the longer the idle the larger the shot. I don’t have to give thought to shot size because volume is controlled by the automatic “dosometric.” On my machine the two on the left are set for single (35ml) and double (75ml) American size espressos, while the two on the right are adjusted at 100 and 150 ml. Of course, these amounts are wholly idiosyncratic and user determined. Mine are set as they are, because that’s what works for me now.
You may have heard espresso cognoscenti argue about the relative importance of the espresso machine, grinder, skill of the barista and the quality of the beans -- the infamous 'Four Ms.' It’s an argument which can never be settled, because it ducks the real issue. That is, (drum roll please) any major flaw anywhere along the chain puts crap in the cup. As pitfalls, they're equal.
Which brings us to one side of the essence of the Casa. It’s without significant flaw.
It’s other aspect is the double edged spotlight the Casa throws on every other link in the chain. It is revealing because it is so responsive. On the positive side, if you're using good coffee, grinding it properly, and have good skills it will consistently reward you with deep insight into each and every nuance. And that’s what it’s all about. More, with the newly added pre-infusion, the Casa doesn't place quite the same demands on filling the pf as the older DT/1s. They were intimidating in their requirement for nearly perfect barista skills, or at least I found them so. The new Casa is not only user friendly but a real pleasure to operate.
The Casa's pre-infusion provides similar advantages to an E-61 group. It makes it a little less brutal than previous Juniors in terms of punishing minor distribution errors, but mostly it just makes for better coffee if everything else is done right. And it is controllable. If you want more, hold the button longer. If you don't want it, don't use it.
I already wrote about temperature control. I’ve had decades of practice with HX machines, including living with a practically immortal Livia 90 for more than twenty years. The Casa is far easier and more repeatable than any HX I’ve ever used – in the same class as an Elektra Sixties or Nuova Simonelli Appia. An important factor in the ease and degree of control is the plumbed-in feed and drain. Using a lot of water makes things a lot easier. If you can’t plumb both ends of your machine, you’re probably better off with something else. Also, balance the facile temperature control against the consequences of inattention.
In Dan Kehn's excellent HB review of the previous, 'non-Casa,' DT/1 he talked about using the 'volumetric' buttons to do his cooling flushes. I use the free pour button, while listening to and watching the flow from the group with the pf out. Then, insert the group, and -- more often than not -- pull the shot immediately. But if I over-flushed, a few seconds is all that's necessary for the water to come back to temp.
Remember the machine's revelatory nature. Buy a Junior and getting by with crap coffee is a thing of the past – painful actually.
With a Casa, you'll NEED a really good grinder. Nothing is too good. Barzata Vario, Rocky.. not good enough.
For most of this “Four M” stuff: User friendly, yes. Consequence free, no. Mess up grinder setting, distribution, tamping, temperature, or anything else important and you’ll know it. Junior can be a harsh mistress. So, don’t mess up.
Some other points:
There is no problem tucking the steam wand against the front panel, it’s a matter of angling the wand as you rotate.
There is no ridge on the steam tip. Rather, there’s a cut creating a flat spot for a wrench to unscrew the tip. The tip cleans easily by running steam in a pitcher of cold water, then wiping the tip down with a clean, wet towel or sponge at least once a day (on days you steam). Cleaning with a damp towel only is not enough.
A lot of people find installing the drain line difficult. As long as you understand that the drain must run down hill for its entire length (no flats, no traps, no “u” bends) and plan accordingly, you should not have any problem. But, as I said, it’s a common complaint. Don't hesitate to get a plumber. It's a difficult concept for the 'Y' chromosome, but there's no shame in spending a couple of bucks to hire someone to do it right.
The “solid bar” on the drip tray screen only causes splashing if the screen is upside down. You’ll never guess how I figured that one out. Or, will you?
As long as the drain tube is properly installed (running down hill), a Casa can not put enough water into the tray for it to overflow.
The machine is actually very quiet when everything is in proper order.
The best way to make an Americano (with any machine) is to pull the coffee on top of the water, not vice versa. Made this way, it tastes better and floats the crema.
The dead band on boiler pressure with a new, properly functioning p-stat is about 0.2 bar (between 1.0 and 1.2 say). As a practical matter, it acts much tighter because drawing water to control temperature gets the p-stat to run in a predictable cycle. In any case, as long as you have sufficient steam, boiler pressure is all about the brewing temp. Otherwise, boiler pressure is relatively meaningless.
The two supplied portafilters are extremely good for the usual reasons. Although also well made, the baskets don't do well with 'higher' doses -- which includes over-filling then finger wiping the coffee even with the basket's rim (about 17g) -- because they lack head room. The Strada (aka VST) 18g basket works better than the Cimbali basket at doses between 15.5g and 18g.
Still more portafilterania: The supplied basket retaining clips are very stiff. If you remove and replace your baskets frequently, the stock clips are beyond inconvenient. Trust me and save yourself some aggravation by ordering a few, lighter springs from Chris or your parts supplier right off the bat.
Bottom Line: It's so good that even though it's very expensive, it's a huge bargain. Yes, it's AN ultimate residential machine. And yes, there are others.
Hope this helps,
BDL

Bought from Chris Coffee. My experiences with them have all been very positive. They handled my sales and installation questions with aplomb.

1 Year Followup:
No negatives, no problems.
The machine is easy to maintain. Run lots of water though it, don't let stuff bake on the head and screen, keep the group and everything else clean. Backflush daily, use detergent (First Circle, Joe Glo) weekly.
Nothing has broken, scratched, faded, bent, failed, worn-out, or..
As far as I can tell the machine doesn't impose any limitations on your ability to extract whatever's there in the coffee. I'm using 18g Strada baskets in the stock pf, and they can be cranky about grind and dosing, however they work better than the stock baskets, so they're worth the trouble. Otherwise, from a 'Barista' standpoint, the only real hurdle is temping, which is true with any HX. Familiarity breeds precision, and the longer I use the Casa, the more sensitive I am to dialing temps in.
Temping the machine is easy. Just so you know: After it's been fully warmed up and flushed, dose and prep the pf/basket , then set it aside for a moment. Using the free pour button run just enough water through the group until you hear the flash boiling stop. Stop the pour, as quickly as you can, at that moment. Give it a second and start another free pour, while counting to keep track of the time. Stop the pour at the appropriate number, and lock the pf in without delay. Your exact count will depend on the machine's idle temperature,. how fast you count and how hot you're choosing to brew. As long as your counting is consistent, you can consistently hit your targets. My coffee choices have me counting to four, five or six.
The La Cimbali makes the point where flash boiling stops very unambiguous and easy to identify, even for people who haven't had a lot of experience. However, experience with HXs in general, and with the M21 in particular, make consistent accuracy easiery.
The improvement in the cup has improved the sensitivity of my palate, which has allowed me to further tweak at the roaster and grinder, to the point were 'exceptional espresso' is a right and no longer a privilege. On the other hand, it's worth repeating that the La Cimbali will not make bad beans better. If you use crap coffee, it will make you suffer.
If anything, my initial enthusiasm has increased.
Yet more follow up: Something bad finally happened. I called Chris Coffee and described the symptoms of a sticking vacuum breaker. They confirmed the diagnosis and told me to fix by wiggling the pin -- as opposed to replacing the inexpensive part or rebuilding it. I opened the machine, was struck by the intelligence and quality of the layout and parts, did as instructed and all was well. The big takeaway for a prospective purchaser should be how incredibly well built the M21 is. You don't see that level of intelligent engineering much.