Teme wrote:pulley / belt slippage and squeaking issue - how bad is this? can one live with it?
I recommend a weekly cleaning routine of the pulley & belt. It takes three minutes. If you do it, there shouldn't be any slippage in normal use. However, you cannot overload that grinder with beans or you are likely to choke it. That was my initial problem. I loaded it to the top with beans and then ran it. The proper way is to turn it on and feed it with beans. I do it in two servings for 18 grams of coffee.
- lack of hopper - is the grind result sensitive to how one pours the beans in?
Yes, see above.
- popcorning - there is no hopper so can one assume some popcorning will occur or are all the beans really "sucked" into the grinder as indicated in the thread
I do not think that popcorn is an issue with the grinder, though I have no way to confirm it other than tasting it in the cup.
- messiness / cleanliness? is there a lot to clean up after use vs e.g. a Mini
I use the Mini grinder tray for the M3 grinder (I cut the two clips that attach it to the Mini). It works well to prevent a messy surface. There is less to clean up because you are not dealing with sweeping a doser clean after a grind session. It takes me about 15 seconds to cleanup after a grind.
- multiple consecutive shots - how does it fare against a Mazzer in terms of the procedure and time consumed?
Here the Mazzer is faster and more convenient. It takes ~ 20 seconds to grind for a shot. The Mazzer will grind enough coffee for 2 shots at that time frame, and you don't need to attend to it as it grinds.
I would naturally also be very interested in hearing any pros or cons that are not apparent from the thread as of yet - can there be any after such an exhaustive report?

Let me try to sum it up in a nutshell:
Pros
1) Near perfect distribution
2) No clumps
3) Better grind quality, resulting in overall better quality in the cup, particularly with high growth acidic coffees.
4) Minimal amount of stale coffee caught in the grinder burrs & housing
5) Practically no coffee is caught in the funnel
6) Esthetically outstanding & unique
Cons
1) No dial scale, though one can fabricate a half ass scale, with hilarious consequences. I'm working on putting together a laser etched scale. (with help from Sean Lennon & Lino). If we are successful, I hope to make it available to all who request it.
2) Takes longer to grind
3) May be too slow & inconvenient when entertaining a party
4) Requires the Barista to attend to the grinder as it grinds
5) Prone to stall if it is not fed properly
6) Requires slightly more time to maintain the grinder - weekly pulley cleanup