I have a "swimsuit" from Koala Swim Wear that has something very similar built in. The differences in the ring sewn into the Koala suit and the Horseshoe are:
- the Koala ring lacks the dimple in the ventral, or underside of the ring
- the Koala ring does not use the dorsal, or top side clip or spacers
The ball/knob features are common to both rings. This feature is very effective, almost magic at helping to create and maintain a huge, raging erection. The balls on the open ends of the ring press into the two veins along the dorsal surface of the cock shaft near the root.
The Koala ring is held in place by the suit's lycra straps, which serve a similar purpose to the clip on the Horseshoe ring. The dimple on the ventral side of the Horseshoe ring is an effective addition - I have a couple of different cock-rings with a similar feature. This dimple presses into the underside of your cock at the base, constricting veinous flow which will help maintain a firmer erection, and may help delay orgasm for some individuals.
I'm going to order one of the Horseshoe rings for a test-drive... for what it's worth, the Koala suit I'm referring to is called the "Blow Me". I think I have a photo of it in action in my gallery photos, if not I'll upload a couple.
I personally like the Koala suit, it's one of my favorite toys and all the people I've been with are fascinated by it. It is very, very effective and I expect the Horseshoe will be as good or better.