I have them on some, and not on others.
I really like them on the smalls. I don't have a problem getting all four fingers on my small Regular, but I do on my small Classic. The lanyard helps with that.
I also have one on a large Regular I carry. I don't mind the looks of a simple one, and I'll use it to pull knife from pocket. I don't have one on my large Micarta, so it doesn't really matter either way on a large(for me).
Don't care for the overly large ones though, and especially dislike the ones with skull beads.