Hi - I ride both my 17hh warmbloods bitless. My youngster (heavy set Dutch warmblood) was backed in a parelli halter, ridden initially in a parelli halter in the school, then I had a sidepull bitless bridle made for him by the saddler who now makes the elevator bridles. He has never had a bit in his mouth, he has good steering and fantastic brakes! My mare, on the otherhand, came to me in a bit, I tried numerous bits on her and finally took the decision to ride her bitless (in a converted elevator bridle made into a sidepull). Her steering is great but her brakes are poor and she tries to lean on my hand, so from the experiences with my guys, i've learned the following:
* don't just take the horse out of its bit and expect it to be able to cope in a bitless bridle (which ever make you go for). The aids will be different in a bitless bridle so you need to teach the horse accordingly
* start by long lining the horse in the bitless bridle/halter to teach them the feel you'll be offering them and what it means to them
* only when they are soft, responsive and understand on the ground should you ride them in the bitless bridle/halter
I looked at a number of makes of bitless bridle before I settled on a sidepull. I dismissed the Dr Cooks because personally I feel they are too strong and don't release quickly enough. The write-ups describe them as 'hugging' the horses head when you take a hold of your reins. Just try putting your forearm into the bridle and asking a friend to take a hold of the reins and see if your arm really feels hugged - I personally found it very uncomfortable and not something I wanted for my horses. I chose the sidepull because it is very soft, looks like a normal bridle at a glance and my youngster never braces against it. However key to having success with any bitless bridle is to make sure your horse understands and is fully comfortable with the feel and aids before you ever get on! Good luck!