I have a recent thread on the QD stripped billet lower, US Army edition. The machining is excellent, very nice lower. I'm considering buying their stripped upper but not in a hurry. I would expect the billet upper receiver would be as nice as the lower but no first hand experience. And I have no idea about the components they use in their complete upper groups as I'd rather choose my own barrel, etc.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek