As I mentioned before, I only keep my cars for 5 years, but every one I had done looked as good as the day I had it installed, when I finally went to sell the vehicle.....and I've used 3M several times, Xpel, and now Suntek. No yellowing, no bubbles, cracks or wrinkles, no unraveling of the edges. The key is to have it properly installed, as mentioned before, and also to take good care of it as you would your other painted surfaces. Get bugs, tree sap, and bird poop off ASAP as they will stain just as they will on painted metal or fiberglass. You can use just about any car wash soap, sealant or wax that you use on the rest of the paint and it won't hurt it, will just enhance the appearance. I've even run an orbital buffer over them with a light polishing compound (to remove swirls or light scratches) without any problems.
The protective plastic film is the best defense for protecting against those nasty little stone chips that will pepper your front end until you get it repainted if you are as fussy as I am. Today's water based paints tend to be softer than those of yesteryear.........just go any auto forum and read the threads complaining about how easily the newer paints chip compared to older ones.......(shrug)