re: experience with the manufacturer
I own over a dozen of their guns in every configuration. It's taken me several years to amass that, and if I pull out all of my MPA MAC-10's, I can track their constant improvement and upgrading. 2 of them are from their first or second build with low serial #s and look a lot different from the current build which makes my mouth water every time I take it out of my safe.
They are relatively small, with their design, test and cnc manufacturing effectively all done "in house."
Once, they had a batch of firing pins that were over hardened, and I know of one guy who had the pin break (there used to be a MAC web board loaded with MPA owners, but the domain expired). He called MPA and they sent him a few replacements. They have a reputation of fixing any problems like that in a timely pro customer sort of way.
The screw on extensions they are now making for the 9mm M-11 pistol are nice and long, and milled from solid aluminum.
Things they've re-engineered which beat the MACs from the 80s:
Their charging handle does not spin around like the old M-11s did;
Their M-11s take Sten mags instead of those old plastic mags;
They mill a piece out of the right side of the bolt, at an angle, for reliability;
They got rid of the ball bearing mag release, in favor of traditional button at bottom of mag well.
I'm keeping my ones that they made
during the AW ban, because they engineered this cool clamp on barrel extension (because threads on a heavy pistol were "evil" for 10 years).
This one is the "side cocker" with scope mount, which is kind of unnecessary if you ask me (but nifty with a red dot on it!):