The one on the roof makes it look like a taxi or a Ford Transit Connect clone. Not sure it does much for you, mine came with it. The ones on the windows are useful and I like them, always put them on my cars.
oh, okay side window visors, yes I have those too. Don't see the point of the one of the roof as mine already has a built-in air-deflector and I find it works very well. Not sure if the 2011 models are different with their sunroof.