Well, I've got 3 sets (including a .308 M5E1) with one of their Freedom edition lowers on the way; so I might be a little partial to them myself. Their AR15 receiver sets are top-notch and some of the features (like the captured rear takedown spring, the bolt-catch screw, and the tension screw) make for some nice kit. I'd rank them as better than average quality. The fit and finish is excellent, with no slop between the upper and lower.
I really, really like their "enhanced" uppers with the proprietary handguards; they are rock solid. I believe the Seekins MSAR handguards also fit these receivers as well.
One caveat...Their M5 (.308) receivers had a couple of parts related hiccups when they first came out, but Aero quickly took steps to rectify the situation and most owners (myself included) have been very pleased with them as well.
As far as I know, their parts kits for the M5's have now resolved all of these issues.