I just ordered "Forever Black Bumper" for my JK, because my bumpers are all... crappy.. looking. Dull. It's what I hated about my Grand Cherokee, I had the same issue. Clean it, lasts for two weeks, back to dull.
Anyway, has anyone used this stuff? I just ordered it 10 minutes ago, I'm curious to see what it can do.
I used it in the past on my old VW Rabbit GTI's black fender flares. You are correct it dies the part - kind of like liquid shoe polish. And like shoe polish, it wears off after awhile and you have to reapply it since the surface isn't really porous. I think I did it 2 or 3x a year on that car. It is an ok product, but when applying it can streak and can be hard to get a consistent finish and I think it can look worse when it wears off than it would have if you had never used it. Of course faded fender flares looked the worst!
I would try it in an inconspicuous area first and try it out for awhile before treating the entire bumper.
It works. I like it! Restored son's TJ nicely. Need to reapply about once a year or a a little more. Use masking tape, DO NOT GET IT ON THE PAINT. (If you do, you'll be using buffing compound to remove it.
I also 'repaired' the end of my JK front bumper after it kissed the car port (don't ask... I feel dumb enough ). I returned the white crease-like mark to black, and stayed that way.
I think you'll like it.
Normally on the JK, i have been using 303 about once a month too. But serious rains will wash that off pretty quickly.
I use Turtle Wax Ice on all the black bits. I really don't know how long it lasts because I reapply it frequently. It does a great job of removing mud stains that won't come off with soap and water. It is "Formulated with light stabilizers to protect your carís finish from the suns damaging UV rays." Besides, it's cheaper than 303 which I also own.