If you still use a desktop computer for getting most work done, then you also care about hardware peripherals like mouse and keyboard. But some people, such as myself, grow out of mouse and need a trackball.
Kensington Expert Mouse is, in my experience, a far worse option than the half cheaper Orbit® Trackball with Scroll Ring. Both have a scroll ring, but scrolling on the latter is far more care-free. On the former device, the scroll ring feels precarious and moves by nudges instead of sliding easily.
Moreover, the form factors of the devices differ. The Trackball with Scroll Ring is designed like a pear over which you can lay your hand, while Expert Mouse is designed like an uphill battle. The wrist position, in my experience, feels far more strain-free on the Trackball with Scroll Ring out of the box. With Expert Mouse you can somewhat approach the same comfort when you turn the device around, the high end towards yourself, as pictured.
Granted, in the picture the Expert Mouse is positioned in front of the keyboard, instead of to the left or right. Anyway, this is the position I find most comfortable when I use an ambidextrous trackball and I am keeping it this way. However, this position requires that some functions on the Expert Mouse need to be reconfigured.
The entire configuration can be done with xinput. The first step is to identify the device name.
In the output, find something like “Kensington Expert Mouse”, provided that your device is Kensington Expert Mouse. Then do:
xinput list-props "Kensington Expert Mouse"
In the output, note the options provided and also if the options are enabled by libinput or something else. In my case, it is libinput.
If you use it the high end towards yourself the way I do, then the most important thing to change is the rotation of the ball.
xinput --set-prop "Kensington Expert Mouse" "libinput Rotation Angle" 180
Additionally, you may feel like keeping the left-click for your left hand and the right-click for your right hand.
xinput --set-prop "Kensington Expert Mouse" "libinput Left Handed Enabled" 1
If you feel like bringing the main two click buttons closer to yourself, the entire set of buttons needs to be remapped. I have ended up with the following line (in conjunction with the two previous lines).
xinput --set-button-map "Kensington Expert Mouse" 2 3 8 4 5 6 7 1