JP Ent., anything I've ever gotten from them over the years has been top notch. I barrel my own uppers, but I only use their carriers and bolts anymore when I can help it. They work way better than any I've ever used and I consider them well worth the extra price.
In fact, I've never heard anyone knock their stuff, ever, and that's damn rare in the shooting world. Some don't like the "cosmetics" of them or may not like a certain feature (I don't care for side charging handles) but they've generally got something for everyone.
They're also notorious for trying new things like those finned barrel heat sinks and low mass carriers and that funky looking brake.