I have one. I don't know how much it does to save the transom. The weight of the motor is the same with or without one and transom is still supporting that weight as you drive down the road. Slowing down on a rough road will do a lot more than any transom saver will. For support to the transom, I have the trailer adjusted so that the transom is sitting on top of the rear set of rollers on the trailer. The reason I have a saver is for the hydraulics. The factory stopper isn't that strong and this one takes the place of it. The hope is that it saves the seals in the hydraulic system when there is a bump on the road.
http://www.iboats.com/Swivl-Eze-Lock...-view_id.37844