Looks like the topic has been well established but I'd like to chime in with another +1 for bca uppers. First, though i do live just a hop and a skip away from their plant, I've had an order process and deliver in under 48hrs. Then I lost the half moon screw that goes in the back of their side charging receivers, where a charging handle would live in a standard milspec upper, and they had x2 in my mail box 3 days later free of charge.
I have more than a few but less than plethora of their .30 caliber offerings, and they've all kinda just worked for me. The -previously pictured- is my favorite due to taking down a lot of bacon and 2 bucks with it to date. It now serves as a plinker and a fun, not my lifeline reciver, way to give friends and family the giggle factor of shooting suppressed 220gr .300blk.
I have had to replace the bolt twice in one of my 7.62x39 bcg's(the second time I bought a Faxon bcg and the jury is still out due to round count) and replaced a few firing pins(of which they sent me new ones every time free of charge) but otherwise my various uppers from them have been suspiciously well functional, and comically inexpensive.
I wouldn't leave one out to join me in addressing a bump in the night, and I'd shame anyone who does. But for a baller on a budget like myself, they sure have worked well enough to keep a browser tab open to their website so I can check in for sales. I've never tried to remove a barrel on one, but a 7.5" .300blk upper had the barrel nut come loose in under 100 rounds once, so now I check that on anything I've gotten from them, but so far, it was a one off instance. For me anyways.