With your wheels being ceramic coated, you should only really need car shampoo to clean them right? If that in itself is no longer removing the brake dust/cleaning them, then its safe to say your ceramic coating is no longer effective, thus it won't really matter at that point (of course, I would hardly clarify a ph balanced cleaner such as P21S harsh).
My vote is save the wheel cleaner until you get to that point a year or so down the road, and stick with car shampoo for now.