I have the Agostini version. It looks like the one MG Cycle sells. It works well at deflecting wind and cutting down on the turbulence (better than stock anyway). In the highest position, I can look through it without much distortion.
Still, you will get the least wind turbulence by removing the windscreen altogether (though you will encounter more wind on your body). Short of that, you may want to try one of the Cal Sci windscreens with a hole in it.
Me, I am first going to try cutting down one of my two stock windscreens to almost nothing. In my limited experience, not having any windscreen at all produces the LEAST turbulence, followed by a large windscreen that you have to look though. A medium-sized screen that you look over produces the MOST turbulence.