If you are determined to try one there are a few things to remember. Buy the absolute best you can afford. Not the most expensive one but the best you can afford. The reason I say this is not all bosals are created equal. Some have rope core which are fine. There are some out there that have a wire inside to give it shape. These are the ones that have given some of the bad rep for the rawhide bosal. Also when looking you will see some that are 8 plait.12plait, 16 , 18. Basically the more plaits you have the smoother the outer surface will be because they are smaller strands and the edges are thinner. The smoother the bosal the less rubbing you get. You also need to shape the bosal to fit the horses face. A horses nose is not perfectly round, the bosal; comes pretty darn round. Ussually to shape it you get a peice of wood shaped similar to a horses face. Kida squarish and tie the bosal around the wood to give it a bit of squarness to go over the nose. There are also different sizes of diameter. Usuall from 5/8th down to about 1/4 inch. Start with the big one and work down to a smaller size. If you try to start a horse with the 1/4 inch he'll pobably just ingnore it. The weight and feel of the bigger one will be where you cues and feel will come from.
One big thing to remember about a bosal is it really shows what not to do with your hands. A rider can not be heavy handed with one at all. A horse will learn to walk through it very quickly if he can. You will ride a horse with body positioning much more than your hands with a bosal or you'll get run away with. One way to not get heavy handed with it is to never pull with both reins at the same time. To stop the horse start with the body position. That is you initial cue, then bring in a one rein stop. It's when people start pulling with both reins that you'll start seeing problems. Of course that can go for bits as well.
This is just some things I have picked up about bosals but I am no hackamore man by any means. I'm just trying to work my way up to it.