It's been debated over and over, some say there is, some say there isn't. Most can't tell any difference. As a side note, many small electrics have the flybar ontop rather than below, such as the blade CP, Hornet, etc.

The usual argument is that with the flybar on top, the flybar won't interfere with the downwash of the main rotorblades providing a smoother flight because of less turbulent air entering the rotor-area, this theory might hold up, of course, aslong as you never apply any negative pitch. Once you start to apply negative pitch, then it goes out the window. So it just sort of comes down to personal opinion I guess.