I have had the weather tech film on my headlights (not fog lights) for two years with no problems.I bought some from WeatherTech and just took them off. They came with the fog light film as well. I took them off because on the fog lights the center was burnt from the light being very hot. It made it look horrible, so I decided that I won't be using anything like this anymore. Luckily I just transferred and now live in a house instead of an apartment, so both my Honda's are in the garage.
Most of these products work, in that they are UV blokers.. but like anything under UV they too will degrade over time. Basically they give their life protecting the plastic lens on your headlights.That's what I figured... I was just hoping that at least one of them was worth it.