Ultraviolet (UV) rays from the sun damages plastic. All plastic exposed to the sun.
The only difference between brands is the quality of the plastic used, and the rate of damage. But all plastic suffers damage, especially on the roof.
We use the all white cushions, and have the MaxAir Vent covers. The thermometer shows that it is about 7 degrees cooler in direct sunlight under the vent with the cushions than without them. Saying they don't help is like saying double pane windows don't help.
But they aren't magic.
And everyone needs to check all the plastic on their roof at least once yearly. All my vent covers come off for cleaning and inspection once a year. They, and anything else, get replaced if the plastic shows any signs of discoloration or brittleness.
