Grinder does a great job grinding, but the chute design leaves a bit to be desired.
Positive Product Points
Worm drive makes minuet grind adjustments very easy. Very solid feeling. Hopper trap door makes purging easy if you need to empty the grind chamber. It also lets you weigh the filled hopper to determine your per shot bean usage.
Negative Product Points
Grind tray way too small. Grind chute not shaped well (doserless version), significant amount of grinds retained. I use about 21g of beans for every 16g desired due to purging/brushing out spent grinds. Power switch rubber cover functional, but not pretty. Worm drive makes coarse adjustment very difficult, making the grinder espresso only.
I really like the solid feel this grinder has. It's surprising how much of a difference a 1/4 turn of the grind screw can make. I love being able to really dial it in. I have this paired with a breville 800ESXL and am very happy with what I get in the cup. I'm sure this has a lot to do with the grind and fresh beans.
I bought the doserless version because I wanted to grind exactly what I wanted on demand, however the chute is rather long and not a straight shot from the burrs. This leads to a significant amount of grinds retained in the chute. I use a chopstick to sweep out the primary chute while I grind, which helps, but quite a bit is always unreachable so I end up purging a little bit before each shot. The chute is also rather large in diameter causing the grounds to miss the basket a bit.
I am very happy with this grinder. Only other grinder I've used in this class is the baratzza vario, and I much prefer the sturdiness of the M4 and its worm drive grind adjustment. I do find myself wasting 20% of my beans though with the M4.