The bosal is called a cowboy hackamore. It's nothing like the mechanical hackamore.
You can find something about it in william langdons book "bits and bitting manual".
If you look for one, only get the kind with the rawhide core. Never use the metal core type. It has to be wetted and shaped to the horse you use it on. This can't be done with the metal core.
This is a very good tool in the right hands and not so good for others.
Find someone who knows how to use this tool to teach you, or just use a good full cheek snaffle to start your horse.
You should find more on how to use it on the web.
Without knowing how to use this tool, you will just confuse your horse and yourself.
I use a bosal on my mare, but she is a been, there done, that nearly 29 year old horse... She never used a bit, she was trained and raised on a hackamore, but she had a bad habit of grabbing the "arm" and pulling, and I was afraid she'd hurt herself, so I got her a bosal, and never looked back. I also have a "Bitless Wonder" for my daughter's pony, if you feel that you're not comfortable with a bosal.
^^ Those look very similar to an indian hackamore. I only have one question though. How quickly do they release the pressure when the rein pressure is dropped? It doesn't appear to me (just from looking at pictures) that the straps would slide back to loose without being pulled back through.