I can only speak to my limited use of the MP5 mag lower of theirs I built. Build quality is decent enough. The extractor on mine is good but a friends came loose on the first range session. Locked his bcg up pretty good. Simple enough to fix but couldn’t have been tightened to spec from the off. I used a Colt LPK with an ALG QMS. Had to switch to a Daniel Defense trigger to solve an issue. Not sure what that was about as the trigger was fine in a 223 AR.
I used their upper and mlok rail with a BA barrel and Spinta BCG. The upper is nice and the rail pretty inexpensive. It does the job for me with no frills and was an easy install. My friend went with the side charging upper. I shot it and it is pretty handy but feels like something that could fail. Or maybe I am biased to a regular charging handle?
As far as the Glock lowers, they are pretty popular locally as the store is here. Everyone I have come across speaks well of them. Hope this helps a little.
I can speak about New Frontier Armory barrels………….They are of good quality, work fine and with that said I would think their other products are decent as well…………I do have a QC10 Glock lower and have used it with three different uppers………never a failure to feed or eject…….their last round bolt hold open sucks………I took the LRBHO parts off and put them away in the parts bin……….The QC10 lower is off good quality, they are pricey compared to the others out there…………If you want a decent BCG, buy FM products, they are like 100 dollars at Brownells and they are awesome……….no issues whatsoever. I have Colt style and Glock style from them………….Yankee hill Machine is making a reasonabley priced Glock lower…everything I ever have purchased from them is top quality.
Should be GTG………I have two foxtrot mike Bolt carrier groups in 9mm ……I was told by FM products the Colt bolt will work with Glock. The Glock bolt will not work with Colt………I paid less for the two BCG’s than I did for one from another company three years ago………lol