I have the AF49 on my Husky TR650. Very happy with it.
Fiddly to set up using the universal mounting kit but works very well once fitted. I like the feature where the top screen can be raised or lowered using the two clamps. It was very easy to adjust to my height (I'm 180cm tall) and no discernible effect on handling or stability. Should be even better on a Guzzi with it's lower centre of gravity.
Have been tempted to swap it over to the T4.
Happy to recommend it, and if a model specific mounting kit is available for your Stone, even better.
