ah that sucks, rode my horse in one today as we have been having bitting issues and as she likes and works best in a pelham i thought I would try a double and she was amazing in it so was going to try some dressage in it, prelim and novice she would be fine in but she may struggle at elementary
Glad you asked this because I was wondering the same thing. My mare leans on the bit loads, crosses her jaw and then doesn't come together very well (feels like her back end is desperately trying to catch up with the front at times). My instructor suggested trying her in a double bridle for schooling and she goes lovely now. It's the only thing we school in now. I'll have to put my thinking cap on again!
i have had loads of bitting problems with my horse too. Had him in a french link, snaffle etc etc. Tried him in a double and much better, but as cant use that in novice tests had to try something else - put him in a hanging cheek and the difference was amazine. Also had problem with him working behind thoroughly, and with the hanging cheek, he came up off my hand in and his back end actually started working properly. Definately worth a try!