Works well - Raven Concealment TopStop Upper Receiver Cover

I'm generally happy with product function as it provides a snug and secure fit on my POF-USA, PWS, and BRO upper receivers to keep the BCG and charging handle from sliding out during transport or storage (previously, I had been using some thick rubber bands to hold the BCG in place). I think it's overpriced for a piece of plastic though, but there's not really any comparable options available unless you have a 3D printer to make your own.