i bought a complete slide set from them. went together with no problems. quality seems pretty good. customer service was good. unfortunately i haven't had a chance to shoot it yet.
I had a few issues with mine but customer service was good. Barrel with an out of spec feed ramp/sharp chamber mouth (appeared that the manufacturer didn't finish machining it before nitriding) and the incorrect Spring Loaded Bearing which was causing failure to go into battery since the extractor couldn't open enough. Easy fixes on both, I spent some time working over the feed ramp and then bought a new SLB for $5 shipped.
80PBuilder's (then 80PercentGlock) customer service was very good and the owner replied to me immediately on a weekend. He offered to replace the barrel ASAP the following Monday but by that point I had already fixed the feed ramp so he gave me a small rebate to compensate me for the out of spec barrel. I didn't figure out the SLB issue until months later but it was a cheap and easy part to replace.
I'd probably buy from them again since the customer service is good and I know what to look for while expecting the possibility of a few defects. The only other issue I see is that they were using 1:16 barrels when I purchased mine which may or may not be an issue with the longer bullets, not sure. I've read online (so take it with a grain of salt) that 147gr+ bullets like a faster twist so I'd probably use a different barrel if I were to decide to build a threaded suppressor host since OEM Glock is 1:10.
One LPK trigger is horrible but I don't think it's 80PBuilder's fault. It's function but has so much creep and grit.
I 100% would buy from them again. Everything was fast, as advertised for the most part, and good prices. My 19build is everything buy the 80% lower from their site and the gun is great!
SWIM did a 34 and it worked just fine, as soon as it went together. Granted, SWIM only bought the 34 upper, so no word on quality of the LPK's but other posts look good.