Ok, what do you want this product for? Are you wanting your horse to 'arch' it's neck, or are you more concerned about how it is working through it's whole body - forward, engaged and through the back?
If you're looking at just getting a 'headset' (the product name of the above link makes me cringe) then don't bother. Learn how to help the use use it's body in order to come 'through' to the bridle, THEN your 'headset' will come.
If you're looking at something to lunge your horse in, to help it come over the back, this product *may* help, but something to the bit is going to be more effective, to the cavesson you don't have a connection in front.
The pessoa system is very good for working on the horse as a whole, it encourages the hind legs to come under the horse and the back to swing, while working into a nice even contact. There is no pull on the horse's mouth and the hind legs move, as the ropes are on a pulley system so that when the leg moves, the roller just slides along the rope rather than straight to the bit.