I messed with one today... the main buttons are... um... wierd? You can't really feel them. The two side buttons are an annoyance, because of the strange low-acceleration of Apple mice and OS X, you have to very often pick up your mouse and move it. It's especially bad when dragging, and you need to keep the button down, but there's no place to hold now that there's side-buttons. I guess they intend for you to us click-lock?
I dunno. Seems like just a regular 2-button scroll mouse might have been a better starting point.