I fitted one not that long ago. I'm yet to feel the benefit but to be honest i bought it because you can see it through the rear window
not because i expected it to do anything. One thing to note that it doesn't show on any images, anywhere. It's a two piece design that screws together in the center of the cross bar, could be a deal breaker for some. Also if you do get one, fit it on a cool day. It's a frustrating bit of kit to fit,
you'll get angry, you'll shout you'll swear and if you've got sweat pouring down you're noggin at 2 litre's a minute due to a baking hot cabbin it's likely to tempt you to take your own life.