P21 is a German product that is safe for our wheels. Nothing will get off the brake dust without at least a quick wipe which means running your hand in, through and around the spokes. Careful as you can cut your hand in there. The wheels have a coating on them which can/will eventually start peeling. This is why you don't want to use anything to aggressive and probably why a pressure washer isn't a good idea if you have any stone chips the blast could cause further peeling. P21 comes in a gel form now which stays on a bit easier.
Not to flame Griots but I have never liked anything from them. It is overpriced and over marketed. Check out the "how to" articles on carcareonline.com. All you ever need to know about detailing your ride is right there at that one link.
2013 X3 Msport, White/Black Montana, M-Sport/Prem Pkg, Dynamic Handling, Xenons, Cold Weather, HU, Prem Stereo