I have them for about 2 years. I have the same experiance with them as tgbol mentioned. .
They didnt change the brightness at all, or atleast I didnt notice a change.
The ones on my foglights are full of bubles.
My headlight ones stayed buble free. But the edges did collect dirt and there is a noticable dark line around the outer edges of the cover. If I remember right, the instructions tell you to start in the middle? I found it was better to line up the cover and get familar with the fit. Peal off the 1st 1/3, line up, start from the one end and push it on, running the bubbles to the unpealed part... then you can continue unpealing and smoothing on. I tried the start in the middle with it totally unpealed. . I didnt have enough hands for it not to stick somewhere where I didnt want it to.
You can now get the new headlight lens assy for about 100 bucks mail order... . I don't know if these lens covers are worth it anymore. With the bad bubbles on the fog/driving lights and the dark outline around the headlight covers, I'm thinking of taking them off.