I don't have many years on my RS yet. However the Xpel ultimate does have a 10 year warranty against yellowing.
As far as color goes, it hasn't started to yellow yet, and my car does park outside all year round. So it gets more than its share of UV.
It'll be 3 years this May.
It has saved the car from nasty stuff, however, it hasn't stopped everything. Mostly on the bumper is where the big stuff hit hard enough to pierce the film and dig deep into the plastic. But nothing has hit hard enough on the hood, or fenders to actually hit the paint under the film. From the few tears in the film, if the film hadn't been there it would have dug into the paint pretty good.
I don't have any clean pictures from this year. But some from last last year at the GLD rental that
SpeedSpeak2me took.
Covered areas are:
XPEL Ultimate = Full Hood, Full Fenders, Mirrors, Full Bumper Cover
Black grill section is covered in XPEL Stealth because it's a matte finish from Ford and I didn't want it getting glossy compared to stock. So the Stealth makes it look 100% like there is no film at all.