To begin with, a cheap bosal will do more damage then good to your horse. The cheap ones are not made well and in untrained hands will be as severe as any severe bit.
My horse, Bonnie, goes well in a bosal and that is all I ride her in. She was trained in a bosal and I have soft hands that have been trained to use one properly.
If you Google bosal, you will get a lot of good information. A bosal needs to be shaped to your horse and tied properly with a mecarte. Your horse should also neck rein well. Bonnie fixed 10-27-12.jpg