I've heard all sorts of whining about SBR AR-15 unreliability but I've had flawless functioning out of my 2 no-name 10.5 inch uppers I bought from FTF Industries. I rarely clean them as they're range toys, I run the crappiest cheapest ammo through them (everything but Tula) and I've never had a single malfunction through at least a thousand of rounds on each.
Your milage may vary, but I'm totally satisfied with my 10.5 inchers and if the Zompocalypse happens, I'd fell rather secure with them. Though as others have noted, the muzzle blast is impressive to say the least and I'd consider a Noveske KX3 as one of mine has.
"Our contract called for 16 cases of rifles and ammunition for $10,000 dollars, not a machine gun...........That is our present to the General"-Pike Bishop