First of all I love them! They are my favorite Mod to any Mustang. I have driven my friends Mustang with them and they aren't too bad if you ask me. You can see out the rear, but definitely not, as good, as you could before the louvers.
Honestly it's not too terrible. Install is a piece of cake, it does take two people, but I would say go for it.
On a side note the Aluminum louvers are the best, I couldn't image getting the plastic ones. Nothing wrong with that but the Aluminum are awesome.