Sometimes its easier having the curb. In fact I just bought a butterfly to use on my horse for CDE events, we are competing at training level and my horse likes to canter, I have tendinitis in my hands and sometimes she gets strong pulls a bit, my horse also HATES single jointed bits with a passion, she hates a straight Mullen also. I do have a ported myler knock off for breed shows and most driving but sometimes we need a little more. The curb also allows for less hand movement on my part. It really is no fun trying to drive a dressage test with your fingers and hands completely numb, or when you are out in the hazards etc. My horse is very well trained, she just gets excited. In some cases, for ADS driving and general purpose driving some horses are trained with a curb, if you never plan on going in the show ring what does it matter what type bit you have, as long as you aren't ripping the horses face off, or the horse isn't running away with you. I found the butterfly type bit at Iowa Valley Carriage Company, I could gush and gush over them but I won't, I will say the customer service is excellent. They do have the biggest selection of mini sized bits I could find though.
Karen