Good lowers. Check out the industry forum here
CavArms for a lot of info.
I got one primarily to make a .45ACP AR. I love it. I went ahead and got a 20" 5.56 upper for it, too. Very solid, good to go in my book. The only thing I didn't like about it was the chintzy butt plate. I replaced it with a DPMS all mil-spec butt plate. (To be totally fair, the butt plate that comes with the CavArms lower would probably last a long time, especially if you're just shooting at the range. But I'm used to mil-spec butt plates and the little piece of rubber that connects the trap door to the plate just wasn't doing it for me. JMO.) At any rate, the lower is good to go! Made out of the same type of plastic that polymer frame pistols are made out of, it should last a while. CavArms has run over 50,000 rounds through a lower and it's still going. I heartily recommend them.
In .45ACP (with CavArms hand guards):
And in 5.56 with CavArms hand guards:
My advice: Buy one!
Hope it helps.