Mini-mags have been great, no issues. I did buy a bulk 550 rounds Federal box and took it to the range. Full magazine with 10 rounds, the first 2 or 3 guaranteed won't eject properly. But if I load 9 federals with 1 mini-mag to start the magazine, 10 out no issues. I'm at the early learning stages with the mosquito (and guns in general) but if I had to guess, I'd think that the federals worked best when the gun is a little heated up from the previous round which is the reason why the first few in a full federal magazine would be the only duds.
With break in mine did "get better." Most problems I had were FTEs as well. Real pain in the ass, but on the bright side, you're working malfunction drills without knowing it's coming in advance.