A Bosal will have less leverage and different pressure points than a mechanical hackamore. I would say in general
that a mechanical hackamore has more stop to it, unless you have a very well trained bosal horse. A horse can run through a bosal pretty easy if they are so inclined.
In general, the shorter the shank on a mechanical hackamore, the less leverage and the gentler it will be. The softer, wider and flatter the nose piece, the gentler it will be. Any version can really hurt the horse with bad hands of course and if set too low, can cause actual physical damage to the nose.
I love this herm sprenger one, short shanks with flat soft leather noseband and curb strap. I use it all the time on the trail with great results:
and I have this Classic Equine Gist Clover one with flat leather wrapped over metal, medium length shanks and curb chain. It is still in the plastic with tags! and I am going to sell it:
It is very pretty and well made, but I thought is was Black and it is a dark brown antique, so it does not match any of my black tack or horses.
You can use any headstall you like with hackamore, tho they will require a short cheek adjustment. I use a dressage bridle (without the noseband) with my my sprenger hackamore, a bosal hanger (basically a strap with ties) on my bosal and would have used my fancy silver browband western headstall on the Classic Equine if it were black and I was keeping it :)
Then there are the 'S' shank hackamores that I am not familiar with, tho I do see some of the endurance riders using them.
Hope that helps some!