Tried them a couple of times. One not so good, the other very good.
The good one was from Screaming-O. It has a vibrating device built in and it's made of rubber.
Cock rings in general can keep you up once the blood is in but "rock hard" after you bust is not going to happen. You're also not suppoed to keep them on long because lack of blood flow down there is not good, but used in moderation, they are fine.
When left on, orgasms are more intense, and with the vibrating it's even more fun for everyone involved.
