I've got a mate with a valeting company who gave me a jar of that stuff once.
I didn't use it in the end as I decided it was gonna be a real messy job that would require a lot of masking. The bumpers on my mates golf have been done with it and they look strange, rather too black. They are also a little bit uneven, I think if you go over an area more than once you start to get a strange finish.
I guess you'd need to try some on a small area first (chin spoiler) and see how you get on.
