Not seen them in RL, but have seen them advertised! Most horse owners nightmare I should think - esp. those that own horses with sweet itch or the like.
Have seen them in RL at Stoneleigh Equine Event a while back. They're like pointy rubber matting but go on the wall. The points aren't sharp. I guess they're a bit of a novelty, who wants a horse with a matted tail and rubbed hair on their bum??