I've had an older Lake Havasu City Bushmaster Carbon 15 Model 21S Pistol since 2005 now. Or rather my wife has. She loves the thing. I was a bit leery to buy it, but I must say the thing runs like a scalded dog. Rarely a FTF or FTE. I do keep it clean and well lubed. It's had several thousand rounds through it in the last 10+ years. So I can't complain about quality or durability. That said, I doubt I would buy another.
I like metal AR's. I can tolerate Glock's, and have 6 of them. But I don't put Polymer or carbon AR's into the same category as the new wave of Polymer handguns. There seems to be a market for Polymer AR's, because they just keep producing them. I just don't see much if any advantage. Especially in a rifle. I think the draw with these "printed" guns isn't the material. It's the idea of making something "they" don't know you have. I don't worry about such things. I guess it's because I've watched people chase government ghosts for far too long.