The rings on the side are used to run the reins from the bit, through the rings to the hands. This gives leverage to set the horse's head and the level of the ring used determines the placement of the head - the lower the ring used, the lower and more flexed the head will be.....................
looks like another instrument of torture to strap a horses head into the correct outline hoping you will be able to reproduce effect when you take it off. Dont do gadgets, there is no substitute for hard work and perseverance. and it shows !!!
I sometimes go to a barn where these (they tell me that they call them 'headsetters') are used on the English Pleasure horses as a matter of course - to achieve this outline: