Bosals, all in all, are advanced piece of equipment, more expensive than say a Little S hack and you have to know how to use one too. They don't offer a lot of lift, plus there's long reins on them and you have to tie them off, which the horse could step through or it could come undone which would be disastrous at a high speed.
S hacks, ed wright hacks, and similar are just a much better option.
The bosal is not meant to be pulled on and it doesn't take long for one to figure out how to run through the bosal if not used properly. You can get lift out of the bosal and that is actually the proper way to use it, with small lifts to encourage the horse to find the balance in the bosal and shift his weight back. You are preparing the horse for a bridle and trying to teach him to stay between your reins not pull him in a direction with the reins.