I recently used the 3M kit on my headlights, i would use it anytime, sometimes it is better however to use the kit along with some hand sanding to help things get better, thats what ive gotta do with mine, the kit was good but wasnt enough paper in it lol but the pads are worth it!
I sand with kit, add extra sanding in between steps if need be with my own paper, then use the polishing stuff in the kit or my own meguires ultimate compound, or both lol then a coat of the wax stuff they provide.. works good.
