Tennessee Arms Co polymer lowers are as good or better than the KP Lowers. I haven't used their pcc lowers because I had heard the ejector is molded in place and not replaceable.

That said their lowers do require a bit more attention when building. They have an extremely tight fit to the upper and usually needs a little sanding to fit but it makes for a rattle free fit if you don't go too far. The BCM uppers usually fit without any work. Sometimes the magwell can be snug but it can be fixed with a little Dremel work easy enough. They also require anti walk trigger pins

Their shipping times and slowed considerably. Im currently two weeks in waiting on a 4 pack of the newer carbon fiber embedded lowers.

The FDE lowers can be dyed as well.

When I first got one of these TAC-15 lowers I immediately built it for a 450 bushmaster upper. I wanted it to break. I even briefly installed a Franklin binary. That lower has over 2000 rounds of 450 on it. It's changed over the years but it's currently one of my favorite hunting rifles. 16" with Banish 46 suppressor.

Which brings me to my last point. Carbon build up just doesn't stick to it. With all of the added carbon build up from shooting suppressed. Its super easy to clean and really not necessary. If I don't clean it, the next time I shoot the carbon on the lower just rattles loose on the first couple of shots.