The logitech Marble trackball is layed out more like a traditional mouse with the trackball located in the center.
It also has scroll buttons located on either side above the two main buttons. The Marble is suitable for both left and right handed users aswell as being compatible with PC and Mac. The forward center position [...]

The most common reason for choosing a Track Ball over a traditional mouse is ergonomics. The track ball mouse allows manipulation of the cursor without requiring the movement of the actual mouse itself. This reduces the users strain to wrists, hands, arms and shoulders that can be expreienced using a traditional mouse. The user can [...]