We used to call them bikini fairings eons ago. I had a Givi, something or other, on my 919. I remember the first time l rode the bike, l was doing 70 in a 55 mph speed zone, and not on purpose. Without the wind blast, l precieved the bike, not going as fast. I promptly slowed down. It was nice to have a little something to tuck behind.
As the other guys have said, you get a lot more noise with the bikini fairing. After l sold the 919, l got a 599, which l like better. I've never put a bikini fairing on that bike. I wil take the wind, with less noise.
But l really like the fairing on that old '01 Interceptor, that l bought last year. It works well. That bike creates a nice pocket of realitively calm air. The Interceptor is a stark contrast that is the calamity that the Super Duke is.