In my experience, horses either do really well with them or they hate them. May I ask why you're looking to switch to bitless?
Here are my feelings on bitless bridles:
- They are misunderstood. Many people want to switch to bitless because a bit is "unkind" to the horse - which is untrue, if you're using a bit correctly. In the wrong hands, even a halter is harsh. In the right hands, the most "severe" bit you can think of is just a communication tool.
- They are not a miracle. Horses still need to be schooled, it won't fix your problems. If your ("your" being used as a universal term, I'm not speaking directly to anyone) horse tosses its head and resists the bit, I would suggest looking at the horse's teeth, the type of bit, and saddle and bridle fit. By checking and correcting those four things, most problems are alleviated. For example, if your horses teeth are sharp and in need of dental care, and he's tossing his head and avoiding the bit and you put a bitless bridle on, he might act better for a little while, but all you've done is mask the problem. *note: some horses genuinely can't carry a bit comfortably - those with odd dental conformation, or a deformity. Also, I would like to point out that a horse with a saddle fit problem is unlikely to be changed much by a bitless bridle.
- Because of the point above, I am leery about looking at horses to buy that have been "switched to bitless." Usually the horse has/had something wrong that wasn't corrected, but rather masked by taking the bit away. Often my first question will be "why is the horse not being ridden in a bit?" and I get answers that lead me to think that there's an underlying problem that wasn't addressed.
- As I said before, some horses are fine/do better in a bitless bridle, and some hate them. Denny (my horse) is of the latter group.
Those are my opinions, and mine alone :) I come from a showing background, so that's partly where my opinions come from as well, where a bit is required to show.