Veteran trackball owners will find the M570's shape very familiar. Logitech makes this clear that it was on purpose: even on its promo page, the company showed that the design is a dead ringer in many ways for models several years old or more. There's a good reason for it, as the heavily sculpted shape is designed to fit a right hand almost perfectly. The trackball, buttons and scroll wheel all fall to hand very easily. Left-handers who can't use a mouse right-handed will want to stay away, but that's true of most trackballs.
Whether or not it's comfortable over long periods is partly dependent on your desk and mousing position. When we first tried the M570, it was actually less comfortable than Apple's Magic Mouse, which itself is known for not being especially friendly to wrists. After adjusting our position, however, we found that it was good for several hours of work.
Our chief issue over a long period is simply noise: the trackball is silent as you'd expect, but the buttons all make relatively loud clicking noises compared to some mice, including some of Logitech's own. If you often listen to music or work in a noisy office you won't mind, but it may be distracting to someone in a quiet room.
Actual motion for the trackball is pleasant; it feels much like a marble and is as price as you'd expect. Be prepared to adjust sensitivity, since your first experience will invariably result in overshooting the target. You may also need to modify your habits for selecting text or other tasks that need drag-and-drop behavior. We also liked that the scroll wheel has clear detents -- a must-have for gamers and anyone else who needs precise scrolling -- though it definitely isn't as polished and pleasant-feeling as the metal wheels on Logitech's MX and VX mice. It would have been appreciated if Logitech had tried to rival its best mice in at least this area.
Read more: http://www.electronista.com/reviews/logitech-wireless-trackball-m570.html#ixzz10sJRnHHg