Having had one on my last Aero, I have to say that it is quite effective. It doesn't stop the wind completely. What it does is stop it battering the back of your head. It's abit like different types of screens on bike fairings change the wind dynamics greatly even though it may only be a subtle difference between one screen and another.
The problem of course is they do not look very attractive. I may have a go with the perspex but I don't think I'd get a standard one again (assuming of course someone made one as my old one would not fit a series 4).
