Flying, just wondering what is the real difference of squared one? I couldn't find one, but I do buy bits at http://www.doversaddlery.com/ They have pretty nice collection of bits reasonably priced, and I can bet they can order one for you too.
It is used on broke (very broke) horses so you can go to the next step in training. Works great on softening as well. They said, "Bit designed to help soften your horse’s mouth and build sensitivity. Use to soften finished horses or start colts." I would not use one to start colts.