if you're talking about this site, it's not shady at all - many members, including myself, have made use of the freetrack option over the years, and i don't know anyone who had issues because of it....
http://www.free-track.net/english/(ps - usually we use it for the head-tracking, and not for the mouse, though - trying to play this sim with a mouse is a bit like trying to steer a car with a monkey wrench instead of a wheel.....