I LOVE this bridle for training or riding a well trained horse who doesn't need something to chew on in his mouth.
The first time I tried this bridle was with a Lipizzaner mare who had been at a "trainer's" for a year before being classified as untrainable. All this horse would do is trot in a 20m circle, no matter what you did with the reins! She wouldn't even stop. With this bridle I taught her to turn and to stop... eventually she could be ridden by my then seven year old daughter - this untrainable horse.
I also start all my young horses in this. It only applies pressure if the rider pulls on the reins. It is perfect for a horse who is tried of a bit. My daughter rode her Arab in medieval competitions (lancing and using wooden swords and steel javalins) in one for several years.
8 year old on "untrainable" Lipizzaner.
Same kid, one year later, showing off her prize for being the youngest rider at the competition on her Arab.
Oh - and other people love them enough that all three that I have bought have been stolen! Which means that I will be buying yet another this summer for starting our new Arab filly.
There are two horses that it has not worked for, one learned to bully through it. The other was very high strung. After years of riding and driving him in this bridle, I switched him to a bit with a tongue toy and he is much calmer.
I have seen other versions of this bit NOT work, this is the one I use.