I just picked up my M-Press. Having read through this thread and a couple of others on here I knew it was a tossup whether I would end up keeping it or not. Have to say, for $120 shipped I'm pretty damn happy with it. The shell-plate thickness wasn't an issue for me and I found a work around for my Hornady micrometer seating die. Basically, just have the handle in front of the die, not returning it all the way back after seating. I just pull one side of the shell-plate aside to release the round. Some might call it an extra step, but honestly can't say it was a problem for me and I sort of prefer that to the auto-release.
Only problems with mine were:
Smothered in grease. Would be understandable on the moving parts, but there were globs on the shell plate area.
Primer tray is kind of a pain in the ass to release. But unlike my old RCBS, it actually works to collect them so can't complain too much.
Missing die block and set screw in another block. Set screw I swapped with an RCBS die, but still kinda pissed they missed putting in a whole die block.
After playing around with it last night, resizing and seating a few rounds, I'm very impressed for the price. I could see people's hesitation with it was $240 or whatever, but at <$150, it's a no-brainier in my opinion. I was pretty unsure how I'd like the floating blocks, but after using it, I think they're pretty solid. No mic to measure runout, but I'd guess it's an improvement from the RCBS single stage I was using before.