I've used some different black bumper sprays recently.
If it's a shiny black satin finish you want Hycote's Bumper & Trim paint is great at looking like new plastic.
If it has a deeper texture then Halfrauds do some bumper paint that's less shiny. See the Alfa bumper where I have posted the Halfrauds photo.
Preparation is key. You need to absolutely ruin the finish of the plastic first with scouring cream and a scouring pad. Any Back to Black residue will cause flaking etc.
if you do what bodger said, with a lot of work it can look very good as per photo (but sort of fake looking in my mind) . its also possible to ruin the plastics if you do a poor job. also whats it going to look like as it ages
if you do what garry said ,it can have that good condition original look. and a lot easier too
on my car the prevous owner did a bad job and the paint peeled. in the end i sourced new plastics and just apply protector
i think it depends on wether you want it to look "hot" now or age well over time
My bumper job was done a year ago and the remarks from a lot of people at the time were just the same as yours (i.e. don't do it) but a year later it looks just as good and hasn't cracked or flaked at all.
I also had the reason that one of the bumpers was scratched and discoloured.
I agree there's no point trying to paint anything if you don't prepare properly. It will look worse.
I also agree with you about not doing it.
Originality is important so if Back to Black does the job there's no point getting the paint out.