So guys..

Haven't used that one but something similar, one bullet vibe rather than two.
It did a reasonably good job of keeping the vibe in place. The material is way too stretchy to really work as a decent cock ring though.
If you're looking for a better item that would do the work of a real cock ring too you might try the Tantus link Vibrating cock ring. I haven't purchased this one but do have the non-vibrating Tantus and I like it.

do they really make u last longer