The Kensington Expert Mouse Optical USB Trackball is a large trackball mouse. The model number of the device reviewed is K64325 and a price range of new mice currently runs from $75-$100. The mouse has a large ball in the center with a scroll wheel (that spins) creating a sort of aesthetic outline for the ball. Surrounding this are 4 large buttons which can be assigned to various functions. The device attaches to the PC via a USB cord. The whole device has a decent amount of heftiness and feels really solidly built. Underneath the trackball is a light sensor similar to a non trackball optical mouse.
The trackball itself accounts for what feels like more than half of the weight of the device. It has an attractive grey color with silver speckles and moves with high accuracy and precision. Moving the ball makes almost zero noise and it is easy to get accustomed to the scrolling which allows for very fast and accurate operation.
The scroll wheel surrounding the mouse turns freely but maintains enough resistance to prevent accidental over scroll. Aesthetically the position of the wheel around the ball is great and the functionality and usability is there as well. Scrolling the wheel produces a slight noise but its not bad.
The four buttons are large (so you can easily operate without fear of accidentally pushing the wrong button). I did experience a slight tendency to accidentally rub the ball with my hand when pushing the buttons on the top of the mouse. This resulted in the on screen cursor moving slightly on the screen which was irritating to me. I surveyed the other people using the mouse and found that they did not have similar complaints. Perhaps my hand or mouse ball technique needs to be developed further. I imagine with longer use of this mouse my technique would modify and it would be no problem.
Overall the mouse is aesthetically pleasing, has 4 buttons + scroll wheel, operates quietly, has very smooth and accurate responsiveness and seems to be very well built and durable. The only complaint I had with the mouse will hopefully go away. We have about 40 of these at the office and they seem to be very consistent in their production with all mice seeming identical both in form and function. I have not used the device for gaming but in the office it functions great. It can be purchased with an optional wrist pad that adds additional comfort.
Overall the Kensington Expert Mouse Optical USB Trackball is a solid choice for a good quality trackball mouse.