Personally, I'm not a big fan of tools that control and don't train.
.I hope it does not loose its effectiveness, and I hope it teaches him how nice it is to walk like a gentleman.
No tool can teach him anything. The training is up to you, the handler. If he suddenly behaved without you doing anything but putting the harness on him, he is not being trained and the bad behavior will return the first time you don't have the harness on him.
Im not sure how it works, but as soon Rocky gets ahead of me the slightest tightnening of leash and he slows up
I would guess
that it is tightening on his chest when he gets ahead of you. I would have to see it though.