Mine with an RRA upper and mag well adapter in an 80% lower I machined has been through several thousand rounds with NO MALFUNCTIONS.
I have been using S&B 115GR stuff for the most part. Went through several boxes of the PMC, 124GR too.
Just NO FAILURES.
I even dropped one box of that WOLF commie BROWN BEAR though one of these. No problem at all.
Maybe hollow points might make these things hickup? Never tried any yet.
But, I think the COLT or the RRA parts and sub assemblies are the best 9mm AR subsystem components to work with.
Anything else like the .45CAL AR I have seen some fellow try to get a group buy going on just have not been proven yet and the bugs are not yet worked out of the design.
For what it's worth?