I would change it so that the leash is much longer, about double the current length. It can always be held shorter by the Domme or links can be held together to shorten it when it is not kept in hand.
The main change I would make is to have the shackles be on a single chain which goes down the sub's back. This way the arms are folded in front of him and the hands are then shackled behind his back. A comfortable position, easier to maintain for a longer time and yet it is secure. He can not reach in front of himself or raise his arms more than a short way up along his back. This is the basic posture used in straight jackets.
I think my version of this contraption would be fun to use as a leash. Walking down a public street it may look like he is just walking with his arms crossed in front of his body. Only a second look would reveal the bondage gear.
