Bosals are often used for training since they contact the horse the same way the halter does, and thus a young horse should already be accustomed to the pressure.
I use a hackamore on two of my mares because both only respond to neck reign, so no use for a bit. However I do use a mechanical hackamore, just in case. We stress repeatedly to (and monitor closely) anyone else who rides them that they must be extremely gentle when applying pressure. But we feel safer having the option for more pressure available if something should go wrong.
One mare has a leather nose peice with that faux sheep stuff inside, the other (that I ride) has a firm (not hard) rubber nose piece.
But my girl's setup will change the day I find something she will respond to.
I think it all depends on where your horse prefers stopping pressure. If it stops for nose pressure, a bosal should be fine
Some are too sensitive to that and a bitless bridal is better because the straps cross under the chin to distribute stopping pressure evenly around the face.
Oops, that was long... sorry :-D