Very happy with my Dart shield, it takes off quite some wind blast from the chest, and the air hitting me is pretty smooth. But possibly more wind noise from the lower part of the helmet, which is remedied by using ear plugs.
My only gripe is the mounting system of the headlight, it seems impossible to adjust the light to the desired position, then the flyscreen. They always seems to want to move together - ie if you try to put the flyscreen more upright,the windblast will push the screen back and the headlight out of alignment. I usually deals with it by pushing the screen all the way back,then adjusting the headlight.