I bought this piece of gear after completing my first 1800 mile ride from where I bought the bike in Tx to home in MD. Come to find out, the buffeting is known for the R1200GSA windshield but it's really bad when passing or following non-aerodynamic vehicles, like pick-ups with ladders on top, mini-vans etc.
I ordered this as soon as I got home for 2 reasons. First due to the reviews that stated how well it worked. Second, honestly, because it's a beautifully machined piece.
So let me tell you the difference. I 've been commuting daily 42 miles RT since I bought the bike back in Mar '11 - over 9000m on her already. I had become accustomed to the quiet, especially when clear road ahead.
I went to the BMW MOA Rally in Blooomsburg and took off the deflector to go attend the Rawhyde - missed out on the training though. So instead, I left it off and went for a long ride on some back-country hard-pack dirt roads and some lovely country-road twisties - wow! The noise! I ride with a Schuberth too. The buffeting was really noticeable. I was amazed how this little piece of lexan could make such a difference.
So for the 5-hr back-road ride home, I re-installed the deflector - man what a difference! This really works. It's so easy to take off and put on. So now for road, I leave it on because it's so much better and for off-road, as you're moving handle bars up, I simply take off the deflector and off I go.
This is a fantastic piece of kit. I highly recommend it for your daily riding and taking it off when going off-road. Much cheaper than buying a new windshield.