ok i'm not going to put a wind screen on my car for sva i quite fancy an aero screen, but when does an aero screen become a wind screen ? size height etc ?

i think when it reaches the drivers eyeline height so that you have to look through rather than over it !!!

In this case, you need to then fit wipers, demister, washers, etc !!!

sound feasable to me. . . . .i'll just leave it off untill i need to put one on

Leave it off for SVA, worry about it after!