I have the Stongard product (headlights only) on my ML. After about three years, it's just now starting to turn a little yellow. It's protected my headlights from at least two large rock hits, and probably many more that didn't leave marks on the material.
I have to turn the ML in at the end of June (lease is up), and I'm not sure if they're going to require me to remove it first. If so, I'll let you know how tough it was to remove (any sticky residue, etc).
Chip H.