You'd have to be going very fast to build up enough air pressure to make a difference. It sticks up about an inch so maybe it might catch some air, but right in front of it you've got the roof rack. I'd be curious to see that combo in a wind tunnel, and I'm sure there would be little or no actual benefit except for looks.
It's all kind of cool and certainly beats the other tuner stuff out there, and you've made a good point about the viewing angle. They should provide a rear view mirror camera and skip to the window all together.
