i personally would not be for a product or device like this.
the cooling out process, in my mind, is very important for the horse and for the rider/groom. not only does it give the human time to observe the horse and ensure there are no issues arising from the ride (lameness, soreness, heat in legs, etc), it also gives horse and human some quiet time to relax together, walking until the horse's breathing and heart rate are back to normal resting range.
hooking up a horse to a machine and having it stand still won't accomplish the above as well. like tying a horse to a hot walker, it promotes human convenience but personally i think it inhibits the horse/human relationship.