I have a Windham Weaponry SRC in 7.62x39. The only issue that I've ever had with it is some light primer strikes due to hard primers. It turns out that the ammo was made in a Ukrainian factory that has since been destroyed by the Russians. Other than that, no issues. I also "built" a 7.62x39 AR15 by combining a Bear Creek Arsenal upper with a Tactical Machining 7.62x39 marked lower that I assembled. The finish matches perfect and it runs 100% as well. I use D&H magazines and RZE Unimags. The RZE Unimags are shaped like regular magazine, but feed 7.62x39 just fine. Here's a magazine review video and me shooting my Windham Weaponry SRC upper on a M16A1 lower.
https://www.youtube.com/watch?v=ma82EphaORQ&t=1s

Personally, I wouldn't spend out the nose on a 7.62x39 AR15 build. The inexpensive stuff runs and if it breaks or wears out, you can buy inexpensive replacement parts. When/if my barrels wear out, I'll just replace them. That's the beauty of the AR-15. BTW, the Windham Weaponry cost me $550 and the total build cost of the Tactical Machining/Bear Creek Arsenal was around $400.