I really don't have anything against clear bras, I just think they are a bit of a waste of money. From what I have seen....

They do discolor over time.
I can spot them on any car, they are not invisible for sure.
I haven't seen one that hasn't started to peel a bit before it was 2 years old.
On cars that sit out in the sun a lot, all it takes is a couple of years before the differences in paint shade is permanent

I've just accepted the fact that I will have to take the time and touch up a chip or two to a point where they are virtually inperceptable if done correctly. For people not willing to take the time, a clear bra is a decent but costly alternative.