UPP stains *some* plastic trim but not all. I've used it on the majority of the S8's plastic with no problems, even used it on the black plastic panels in the wheelwells. But there are a few pieces on it where I *do* get staining. Just gotta take a chance if you want to see it it'll work OK. The *hard* black plastic, shiny surfaces like Audi "B" pillars, shouldn't be a problem. The hard black plastic (actually more of a dark gray) at the bottom of the Audis seems to do OK with UPP too, but watch that you put it on evenly so you don't get streaking. I buff it off with a spritz of UGE or FK425.
If in doubt, I'd use AIO instead and put some 845 on for a topper.