I'm not a fan of the Anon M2. I bought a pair second-hand through this site, so I had no recourse to get a refund... learned my lesson there!
One issue (mentioned prior) is the lens popping out when moving the goggles between your helmet and your face. If you grab them with one hand at the nose (which I do with all prior goggles), the frame flexes enough to cause the lens to pop out. This is remedied by using both hands to move them and supporting the goggles at the edges near the straps. But I don't really like that as a fix since if I am moving my goggles, I don't want the pole anywhere near the lens to prevent scratching. So generally I move them with one hand (poles are in the other). With the M2, I had to plant the poles in the snow/ground, then moves the goggles, grab the poles (which sometimes fall over! bah). It's that or move them while holding the poles, and that's not great in a lift line since you are likely to whack someone.
So yeah, big time first world problems with the first gripe.
But really, my biggest gripe is issue number 2. Lens durability. I don't know if I was given the cheapest crappiest made lenses possible, but it sure felt like it. Bumped them once with my pole handle (the rubbery part) and the finish was visibly marred. OK, noted, they are delicate, so I then became very paranoid, using goggle soc all the time and being very careful. Then one fall in the snow and the coating was scratched badly BY THE SNOW. How do you make a lens that cannot stand up to abrasion from snow? Isn't that all they are really supposed to do? Don't care how fancy the coating is if it can't withstand normal wear and tear (falling in snow is normal IMO). They need some protective film over the metallization.
M4? No idea how those are, but I won't get another ANON product after the M2. Lenses nowhere near durable enough for me and the flexy frame ejecting the lens is a bad combo.
/end old-man-rant