I hate to be that guy, but Leonardo didn't really innovate here: the hurdy-gurdy had existed for a long time by the time he sketched out this instrument, and it had rosined wheels turning against strings, the different pitches being selected by a crude keyboard of buttons. Sure, this is more refined, but all the important elements were present in an existing instrument.

Still, though, it makes a pleasant, musically useful sound. I wonder how hard it is to keep in adjustment; it seems like it would be touchy (just like the hurdy-gurdy).