I tried the Gentle Leader with Seven when he was younger. When he had it on he acted like his back legs didnt work! It was the funniest thing. Without it he would jump up in my car no problem, with it on he would pull himself up in the car with his front feet and drag his back legs up like they didnt work at all! Same with him coming up on the couch (when he asks like a gentleman), he would pull himself up and drag his legs.
I didnt like the Gentle Leader. I found walking him with a tight leash (him next to me) and the command "Stay with me" and praise him when he didnt pull at all worked better. I just reinforced constantly what was good behavior and he got it quickly. I rarely leash him because he "stays with me" when I ask him to, or in sight, and never crosses the street without sitting first and me telling him its ok to cross. But when I bring him into stores its nice not to have him pull on the leash when Im shopping or trying to pay for something!