I use a Kensington trackball in conjuntion with the mouse. I feel both are required. One of the things I really like about the trackball is the outer ring that surrounds the ball itself. When you get into any browser it makes scrolling a dream and much faster.
They are not for everyone. I like it though. There are some operations that you can do rather smothly with the trackball compared to the mouse. It is important to be able to use the left and right click buttons with one hand while you are also using the ball.


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