Very surprised - American Tactical Imports AR-15 Stripped Poly Hybrid Upper Receiver

I have to be honest and say that I bought this because it's cheap and I assumed lightweight, and a bit curious from an engineering point of view. It's $29, so when the receiver got here today I was not expecting much. Was I surprised! It looks great! Does not look like a polymer part. It looks like a quality finish found on forged uppers. The inserts are alloy of some kind, presumably 6061 and I thought of how you're supposed to tighten the barrel in. Sure enough the instructions make it clear to use a barrel extension mount, which makes sense. If you use a traditional outer clamp or other method to hold the receiver, you'll end up breaking something as I saw evident in another reviewer who clearly didn't bother reading the paperwork. Mine required a tiny bit of polymer to be filed off at the rear of the rear lug to seat perfectly (perfectly - zero movement!) on my PSA lower. So far, very impressed!