How much do you rely on the rear sides for view? Pulling out of my neighborhood, I have to cross over into a median (4 lane divided highway). If I had the louvers (really would like to install a set), I'd loos what little bit of rear, andgled vision they provide.
If you do not have this situation, then go for them. If you need to use them for any type of vision, then I'd recommend thinking twice.
Then again, most folks that mod their car do it for looks first, function last.
It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt.