It's nice to be able to scroll in both the x and y direction with the ball. It was positive on the ball, the downside is that it hooks up far too often. Suddenly, it may get the idea that it does not want to scroll up, then the only thing that helps to take a damp cloth / paper or paper to rub against to get the dirt that enters.
Right-click is the little problem with too, just like griphon wrote it will not work forever.
It is at least neat ;)