My model1 7.5" works well- with the right ammo. I haven't tried it in FA yet- maybe I'll do that later today.
Issues that I've come across with shorty uppers are twofold.
First, extractor jump/FTE. Happens in full and semi. This can be mitigated with a #60 "O" ring placed around the extractor spring (perfect fit), or you can get the Wolf extra power spring. Still may not function 100%
Second, bolt bounce. FA only. A heavier buffer slows the ROF and hence prevents (?eliminates) bolt bounce/light primer strike. Again, FA only in my experience.
Interestingly enough, I've had issues (in FA) with the gun not wanting to eat the last 2 or 3 rounds from a perfectly good new mil-spec mag with the green followers. Believe it or not, my el-cheapo steel Taiwan (?sp) mags function PERFECTLY in FA.