Compare cost. I've been running the Shotguns for years. BUT, at WOT they do not provide much, if any, sound dissapation. They are meant to provide noise control at idle speeds. I am told all the time that my boat is really loud when I fly by people. This is with the Shotguns on the boat.
Not all that familiar with the HPI set up. But I would venture a guess they do more for you at planing speeds than the Shotguns would.