I used these to replace the craptastic stock switches on my WE SCAR.
These are a HUGE improvement in my opinion, they feel much more comfortable/pleasant to use. I often catch myself flipping the selector switch up and down while bored.
They're made of plastic, surprising considering the price. Though, they are of excellent quality. Can't see them breaking/failing anytime soon.
The only reason I give it a 4/5 is due to it's price. Twenty bucks is a tad-bit steep for some plastic tabs, I would have liked metal at that price.
I'm very happy with them, and recommend them to anyone with a WE/VFC SCAR.