This review is for the M4 with stepped adjustments and a doser. The M4's current stepless feature, introduced some time ago, was not available when I purchased my grinder.
I bought this grinder about four years ago after reading positive reviews here at CoffeeGeek. I chose it over the Mazzer Mini at the time because of the shorter overall height of Macap; reviewers said it would fit in the typical space between countertop and upper cabinets, whereas the Mini was a bit taller and might not (I understand that the Mini now has a shorter hopper available to alleviate this).
Out of the box: I was very impressed with the packing, the weight, and build quality of the unit; I got the grey color at a discount because it was a customer return for some reason. At first glance I lamented that I should have got the chrome to match my espresso machine, but that feeling didn't last and I like the looks of the grey next to my chromed Quickmill just fine. (The understated grinder does the 'heavy lifting', let the gleaming Quickmill take the credit...)
Step Adjustment: The increments or steps are adequate for my espresso needs, seems like each increment equates to about 3 seconds difference in pulling a shot. I think my tamping pressure is a greater variable than the step size, even after all this time. I don't change the grind setting very frequently for espresso; when I do I usually change by only one step or so. I typically have to remove the hopper and inspect the adjustment collar beforehand to remind myself which way to turn it, for the fine-coarse indications are neither highly visible nor intuitive. I also grind for a press pot, so I've marked the collar at my nominal adjustments with pieces of tape, one marked 'E', the other marked 'P', so I can go from my espresso setting to a coarse one and back again (hopefully) without having to refer to the 'hard to see' numeric scale on the collar. The reader may sense a contradiction here, that my taped markers should overcome the shortcomings in the native markings on the collar...so I'll tell you that when I look at those tape markers, and I haven't made espresso for a while and want to go there from the press setting, I don't know whether to go a quarter turn one way, or three-quarters 'the other'; it's a crapshoot.
Grind consistency: With this level of high-quality burr grinder, there are no discernable 'batch-to-batch' variations from one shot to the next at a given grind setting. You get a consistent grind at a particular setting, period. Changing humidity and the type of roast may cause some variation, but the grinder itself is rock solid.
Burr Noise: I do not think my grinder runs as quietly when empty as other users report. In addition to the motor hum that you'd expect from any similar appliance (like an empty food processor or in-sinkerator purring under no load) I also hear the sound of metal-on-metal contact between the burrs. I do not know if this is normal or not, for it's typically not very loud. But, if I push down on the adjustment collar, or just wiggle it at a particular setting, the noise or 'squeal' increases dramatically. When I let go the sound subsides. This also occurs when I make adjustments while the grinder is running empty; the noise of the burrs increases as I make the adjustment (typically going finer), but abates once the burrs have 'settled in' to their new position. This has not affected the sharpness of the burrs or the quality of the grind after four plus years, so I've not worried about too much and have made no serious inquiries or effort to remedy it.
Parts and Misc.: For safety reasons (I suspect) the hopper has a shield installed amidships (to keep you from poking your fingers down into the grinder). There's another protecting the discharge chute. I removed both of those because I felt they were in my way, and with no kids in the household to worry about, I'm not likely to accidentally make the reach down, or in, to injure my own fingers. I also removed the black tamper foot that extends out front, for I never used that either. The catch tray is tiny and of little use, so I've put that back in the box and replaced it with a Tupperware container (would like to be able to buy a useful tray that fits the contour of the grinder base). I also removed the sliding feed bar at the bottom of the hopper, for I'm not typically changing beans or loading up the hopper.
Doser and Portafilter rest: I seldom have need for the doser because I typically pull only a shot or two at a time. I once took the doser off (a significant undertaking) to see if I could use the grinder in a doserless mode, but its removal left such a gaping, unsightly hole that I thought it best to re-install it and live with it. So I flick that sturdy doser lever a lot just to get my small amounts of coffee out. The doser sweeps itself clean pretty well, but I often take a brush to it and the discharge chute. I like the rounded stainless steel portafilter rest; it is strong, yet sheds spilled grounds, and is easy to wipe clean on the rare occasion I do so. Yeah, it works great for portafilters...but also if I've ground some coffee for my french press, I can set a sierra cup on that same rest and, because the doser lever is recessed, I can operate the doser lever to release the grounds without knocking the cup over. A little thing maybe, but its very handy, and if my memory serves me, other grinders aren't as good in this regard.
Added plus: Filling the grinder with beans right to the top of the neck of the hopper is exactly the amount of coffee required for my half-liter french press, so I just pour up to that spot with no other measuring tool.
Switch: The switch has a silicone cover and, as noted in other reviews, it does make the rocker switch a little more difficult to operate. However, I have not found this to be much of an issue. My countertop is stone, and the surface is smooth enough for the grinder's rubber feet to grip pretty well, and the grinder does not slide on me when activating the switch one-handed. (The grinder does shift in response to the repeated use of the doser lever; every few days I have to slide the grinder a bit, back to its 'spot').