Headlight film?

I know that all cars with plastic headlights suffer from discoloration over time. Has anyone here used the headlight protector film before? I see them on Amazon, and the reviews are mixed. I also see that WeatherTech has them: http://www.weathertech.com/lampgard/
Pricey, but cheaper than replacing headlights, assuming they last more than two years and they actually stay on.