I think this slow start device is very similar to another thing that pops up on the forums from time to time: a gizmo that allows speed control of single phase induction motors which seems to solve all the problems of single phase motors. These are useful in only a very narrow range of circumstances, usually fan control. The soft start mechanism is the same and, I believe, uses the same control mechanism combined with a timer. The technology is not new and if it was universally useful everybody would be using it. I would proceed with extreme caution.
Rod