Let's see if I can explain my take on this....I haven't used P21S all that much but to me it looks a lot like Meguiar's #16, which I *do* use a lot. The P21s might look a little better, but they're close, very reflective and "clean" looking for carnauba.
I had #16 on my wife's silver A8, it looked great. I decided to put 476S over top of it for added protection in the winter. It muted the look, really made it look far less impressive. I was kinda shocked at how much worse it looked, as I really like 476S. I was so disappointed that this last winter I just stayed with the #16.
I still like 476S but that was a real eye-opener for me. I'm *still* surprised that the 476S disappointed me so much....but that won't stop me from putting it on some of our cars