I've been tempted to try them out. They *look* decent and the price is fair. I probably will do so and report back. I will probably go for a plain Jane 5.56. I have a Colt 9MM Carbine and that takes care of my 9MM needs. I pick up random unknown Lowers from time to time to build stuff from left over parts. I'll add that I'm an armorer, which is why I have lots of random parts laying around. If it works out I recommend to people or vice versa. Here's some from my experience:
Aero Precision: Rob the Texan is right about Aero. They're hard to beat for the price. I've done quite a few builds with them with no problems. Anodizing is top notch. Some premium features at a non-premium price. They have some great promos and the blems have always been great.

PSA: I've had some great PSA Lowers and some not so great, as in I couldn't close the takedown pin into the upper receiver on one of the 'premium' SC Lowers back when they offered them.

Noveske: Nothing but good things on first run and chainsaws.

UCWRG: They make an amazing product when you can get them. I have a pre-production Billet Lower that Steve gave me that is a work of art. They also do a lot of research and make improvements over the usual run of the mill spec