Yes I use them. I have a 13 yo ex RS gelding who was ridden in a Pelham, because he was 'strong' and 'naughty'. No, he just didn't like heavy handed beginners hauling on his mouth and said so. He's been in Dr C since I bought him three years ago. We hack, jump and school in it, never a problem with brakes or steering.
I bought a recently broken five year old Anglo Arab and put him straight into a Dr C and he is doing fine. Shook his head a bit to start with - but then he used to chomp endlessly on the snaffle I had to use fo a week before the Dr C arrived form USA. He is quite happy now and very responsive.
I am terrified of my heavy hands and find I can ride and be more relaxed knowing I am not ever going to jag the horse in the mouth. I have used them on three of my friends horses (because of my hands issue) and they have all settled well to them, including a mare who was said to be a nutter and that I would die riding her 'without brakes'.
So, yeah, I like them. They are not suitable for all horses or all riders, but they do for me
i tried one, then bought a Nurtural (v similar but with stabilising disc of leather under jaw), it is very useful for horses which have had the dentist etc, and i've hacked out in it, but wouldn't dare canter or jump a strong horse in it... so far...
made the mistake of riding a breaker in it (early breaking in stable) and when she stuck her head down and tried to bronc me off, i forgot i had the nurtural on and couldn't work out why i couldn't pull her head up! it was quite interesting for a minute or two...! so, i wouldn't ride a bucker in it either!
I loved my Dr Cook and so did my horse. He tended to lean on the bit, but went much better in his Dr Cook. He also had better brakes. Some people say that steering is not so easy, but I didn't find that the case.
Very good comments!! I have just bought one for my pony as she has been riding out in a dually really well. Although I love the dually, It wouls rather the leather look. Thankyou for your feedback.