Uh, what's the theory??

They both protect the bottom of the boat, but I can't imagine both of them together will do anything but make your boat a lot heavier = BAD. Pick one, and go with it. I would go with the coat-it, it's a lot slicker than the bedliner stuff. However, I have a buddy that Armacoated his drifter, and they said they would guarantee it for life, too. So, if you ding it all up, they'll fix it for free....