I had every VerticalMouse so far (they don't seem to last for me for whatever reason). I prefer the C, it sits nicer in my hand, they changed the shape; I can't comment on the buttons as I under-utilize those. Either way though, going to any VerticalMouse from a regular mouse is a huge improvement. The changes between 4 and C are probably hard to pick out for someone who hasn't exclusively used those mice for a decade.