I have a B&T APC45 that I have never bad one malfunction with. I just got my Form 1 back on it, and love everything about it, except the cost of magazines, which led me to cough up $3500 to buy an HK UMP just because it has cheaper magazines! Now I have both, and the biggest problem is deciding which to shoot. :) Usually the Thompson SBR wins.
Seriously, I can't stand the Kriss, so I would never buy that. I've never had a lick of problems with the APC45. If you really, really, really have to have a .45 carbine, these are all great, but spendy choices. If I could only have one, and worried about $$$, I'd skip .45 and go 9mm with a CZ Scorpion. Hardest thing to beat right now. 9mm performs better at range than the heavy .45, and is so much cheaper to shoot. I have an Uzi, a Mk760, a Coharie Mp5 clone...all SBR'd. The 9mm guns just are more pleasant all around.
Still debating whether to SBR the UMP or not. The B&T is more practical. But the UMP is...a UMP. OK, so it's a dressed up USC, but STILL.