Glass balls (marbles) can be used but need to be inserted by an experienced equine repro vet. The idea is to create an environment where the uterus isn't receptive to pregnancy (either it thinks it already IS pregnant or the room isn't ready to accept a bub) either way get some expert advise from a good facility.
Yes, it stops the mare from cycling. I looked into for my mare that was constantly spring heating. I don't like having to give them regumate myself. This was before the injection was available, so I looked into alternatives.