Almost perfect.
I am 6ft and ride a 2006 BMW R1200GSA. I wear a Schuberth C3 for road trips and a Shark Evoline convertible off road.
The deflector and mount are made of high quality materials, well packaged, and with good instructions. Note: half the instructions are found underneath a cardboard base in the packaging. I only found them when I was breaking the box down for recycling, after I had already done the installation from downloaded instructions.
Without the deflector, the airflow hits around the base of the helmet, causing plenty of noise from turbulence. In the summer, I take the screen off completely and it is quiet because the helmet is in smooth air. In the winter, I like the deflector for road trips because it raises the screen and reduces the turbulent flow around the helmet. I used to put the screen on its highest adjustment, but now I put it in the mid setting with the deflector on. This has had the added benefit of improving the aerodynamics in cross winds, because I am a little closer to the screen, so I remain protected a little more in cross-winds. In calm conditions, I ride in a bubble of still air in quiet comfort. It's startlingly effective, especially given the diminutive dimensions of the deflector.
Off road I take the deflector off, for two reasons: first, I want a clearer view of the track in front of the bike. Second, the additional weight of the screen with the deflector on causes it to move just a little too alarmingly when I hit rocks and holes in the track. I am worried about over-stressing the screen mountings off-road with the deflector in place. I leave the metal mounting in place though because it is held on one side by double-sticky-sided foam tape which would be impractical to replace every time I remove or replace the mount.
One thing that could improve it further: it is nice to be able to grab the deflector and move it up and down. For example, riding through town it is nice to lower it and have more air in my face, but on the open road, raise it again. If I tighten the adjust screw just right, I can do this for a while, but inevitably the screw loosens up and the deflector flops around until I tighten it just right again, even if I use thread lock to stop the screws vibrating loose. If it could be engineered so we could set a tightness that doesn't change with vibration, it would be even better.
One more thing: when I placed my order, the website claimed the item to be in stock, delivered in 2-3 working days. This turned out to be false. After 5 days, I emailed the company, and they casually told me they were awaiting stock from Germany, as if this is completely normal - and I expect it is. It took 2 weeks. The company has a lackadaisical attitude to the accuracy of the delivery time, so be prepared for a frustrating wait, made worse by unapologetic customer service.