The Wonder Curb has more bite to it than the curb chains that come with the bits, but it will not cut or leave any marks - however it will definitely get their attention! I carry one of these in the D ring on the back of my saddle just in case I have to make too many fast runs, my horse is getting nervous in the box, or whatever. If I put it on my horses they get in the groove and settle down right now. They seem to know better than to challenge it.
If you're buying one of the Fast Time bits you can add a Wonder Curb for only $20. Discount will be taken in the Shopping Cart.