This mouse if given time is a fantastic mouse. The shape size, height etc may take some time to get used to but once comfortable its a very good mouse.
The middle button and scroll wheel are both very responsive and feel comfortable. The side button which will be tricky at first to use, is not as responsive, I often find I have to click twice but its nothing major, but after a while you just find your self lifting your hand a bit to access it.
The fold up feature is nice but I find myself never doing it, and the dongle which is rather tiny also clips to the mouse under the fold, again I just leave it plugged in 24/7.
Overall excellent mouse but may take some time to get used to and may not be suitable for all.