My BF and I used one from time to time. The ring had a little pouch with a bullet style vibrator. We both loved it, although I think I enjoyed it more as a bottom than he did as a top. It's just like using a vibrator, but during the act. It's great!
edit: Clarify – we used a cock ring. We have seen the condoms, but they didn't seem like they would give off enough vibe.