Finger-operated trackballs with center-mounted balls work for both right- and left-handed people and encourage better wrist posture, while thumb-operated trackballs are more similar to traditional mice and therefore easier to get the hang of using. (For more information, see Should you switch to a trackball? below.)
A trackball isn’t as accurate as a good-quality mouse, but it can be more precise than a trackpad for anyone looking to eliminate repetitive motion from mousing around too much. Although trackballs can help some people with some symptoms of repetitive stress injury, they can’t help everyone—we recommend consulting a doctor first if you’re considering a trackball for that reason.
Source: NY Times – Wirecutter