First the grind: I tested the Capresso by making small amounts of four different level grinds, from somewhat course (as one might use in a flat filter type machine) to an appropriately fine pump-espresso grind. (Note: There was still several more 'notches' of courseness available which I did not try, good for press type units, perhaps.) All were notably more consistant than I have found with my previous grinders. There was, for instance, no build up of "dust" on the ground coffee cannister adjacent to the spout; something I have sadly come to expect from even good quality burr grinders.
Particularly the fine espresso quality grind had a noticable evenness and consistancy. Excellent!
I found that NO grounds or dust escaped the machine on my unit. The area stayed clean; indeed, far more so than with my pair of (admittedly old) Braun units.
Why were my results so different from other reviewers here on the site? I can only speculate. One reason may be a failure to follow the very specific first use instructions. I almost missed these myself, and would have had I not brought the machine home late in the evening when I was not tempted to make a quick shot before reading the manual.
What is explained is this: The machine is manufactured and shipped with the burr faces touching. (Likely for ease of alignment and the protection of same during shipping) Thus, the manual cautions, an owner MUST first use the grinder set to a course grind and only after grinding several tablespoons of beans move it to a finer setting. If this warning went unobserved the burrs may have been thrown out of alignment which, I suspect, would lead it both an inconsistancy of grind and an inability to make a fine enough grind for a pump espresso machine.
The "clogging" and 'dirtyness' is more easy to explain. They would (and possibly did) occur if the machine was not kept scrupulously clean, both internally (the burr wheels and exit spout) and externally (where the grounds receptical slides in).
In the first case the rather small, directed, opening through which the ground coffee passes on it's way to the receptical woul no-doubt clog if the machine was used daily for a week or more without cleaning. But such cleaning is always neccasary for a burr grinder, not always to prevent clogging (some units have a larger oriface), but for reasons of freshness and flavor. Old beans and coffee bean oil quickly turns bitter. It should be removed often. (The Capresso makes that unusually easy thanks to the fact that the upper burr wheel comes out with a twist.)
At the same time if ground coffee were allowed to accumulate in the housing behind the grounds receptical then that piece would no longer fit tightly and, with the protruding output lip not set into the container, no doubt coffee grounds would be scattered over the counter.
Maybe, of course, I was just lucky. Maybe my unit had closer tolerances than most. But frankly I doubt it.
In any case my own short experience with the Capresso 551 grinder has been altogether a satisfying one.