Hi just to chip in here ! I removed my BMW wind deflector, and bought a clear glass deflector (not acrylic but toughened safety glass from a company in Germany, so a lot more expensive!!!).
I bought it not because the stock did not work because they do and very well indeed, but for the ability to see clearly both day and night.
There is no doubt that stock is reduced visibility, especially if you want to see if an unmarked police car following as you maybe moving a little bit quicker, safely of course!!!
The glass deflector is not as efficient as a wind deflector, as with the stock being mesh wind is allowed to pass through, were with glass you get some bounce back, but still very effective. But big win with clarity and to some extent security.
As for those with no deflectors that is there choice but there is a big big difference when you have one, and yes subject to speed also depends how effective they are!!!!!!
I have done threads on this subject before, perhaps on bimmerfest ???