This is a trackball. Period. Nothing more, and nothing less.
If it were possible to turn it over and use it as a mouse, I might understand the name (don't laugh, I already own a Kensington Slimblade Trackball Mouse which can be used as either a mouse or trackball). But you can't, and there is nothing else you can do with it which qualifies for the "Expert Mouse" part of the name, as far as I can see. Therefore, I think the source of the name is clear: Kensington has a Department of Silly Names.
But once you get past the name, this really is a very nice and exceptionally versatile trackball. It has a number of features, both physical and functional, which I think are extremely good and some of which are quite unusual.
Physically, it has a large, easy-to-use ball, which is surrounded by a scroll ring, and four large buttons. By default the buttons function as traditional mouse left, right, middle and... uh... well, I'll come back to that in a minute.
It is considerably larger than I expected it to be judging only from the pictures I had seen of it. As a result of this, it is more stable sitting on the desk.
For those who might want a bit of wrist support or elevation it also includes a detachable (padded) wrist rest. The way that it attaches, and the fit against the main body of the trackball is sub-optimal, though. If you don't need a wrist rest for medical reasons, I doubt that anyone would use it for aesthetic reasons.
The first really clever thing that I discovered about this trackball was the scroll ring. This is a small movable ring surrounding the ball, which serves the same purpose as a wheel on a traditional mouse.
I also own a Kensington Orbit Wireless Mobile Trackball. It has a scroll ring, but it is touch-sensitive rather than mechanical as this one is. I honestly prefer the ring on this new trackball. I find it easier and more natural to use, and more precise to control, especially when I am trying to move it very small distances.
I think the cleverest thing about this trackball, though, is in the functionality. It is a dual-mode wireless device which can connect either via a USB nano dongle (2.4GHz) or via Bluetooth 4.0 - thus saving a possibly precious USB port.
Connectivity is controlled by two switches on the under-side of the trackball base. The one on the left is a simple on/off switch, so you can turn it completely off to save batteries when you want. The one on the right is a wireless mode switch - when set to the right it is in USB 2.4GHz mode, and when set to the left it is in Bluetooth mode.
This is illustrated at least twice on the bottom of the trackball, as shown at right, with a label and with embossing in the case. Also, the User Guide that is included has a few pictures, and short bursts of text in 13 languages (yes, thirteen), so one way or another you should be able to puzzle it out.
Of coursed this dual-mode function means that it would be very easy to use this trackball on two different systems, for example with the dongle on my Acer All-in-One desktop and via Bluetooth on a Raspberry Pi 3. I can see this use case coming on my own desktop already.
To initiate Bluetooth pairing, you switch to Bluetooth mode (duh), and then press and hold all four buttons simultaneously. There is a very subtle blue LED between the left and right buttons (visible in the scroll ring picture above) which will start to blink when it is in pairing mode, and will go off again when pairing is complete. Oh, and this LED will also blink red when the batteries are low, according to the User Guide.
Finally, the four buttons. By default the bottom buttons are the left and right mouse buttons (button 1 and button 3 for Linux/Unix types), the top left is the middle button (button 2) and the top right is a "back arrow" (button 8), for example going to the previously viewed page in a browser session.
The trackball is symmetrical, so it can be used comfortably with either hand. If you want to use it left-handed, the button assignment can be reversed using the Mouse Settings control of whatever desktop you are using. The KDE control is shown here.
If you want to do more than just swap the left/right mouse buttons, the xmodmap utility gives you complete control over each button and every function. The details of this CLI command are rather obscure, but here is just one small example...
Suppose that you are not an old-time Unix/Linux die-hard who is still in love with the three-button mouse, so you don't really need for that top left button to act as the middle mouse button. It would be logical to have those top two buttons act as "forward" and "back", wouldn't it? To do this with xmodmap the command would be:
xmodmap -e "pointer = 1 8 3 4 5 6 7 9 2"
Yeah, I know, that's really getting into nasty geeky Linux CLI stuff, but that's the way it is - and you don't need to deal with this unless you want/need to remap the mouse buttons beyond simply reversing left/right order.
When the trackball is used on Windows or Mac OS X, there is a Kensington Trackball Works utility to customize the button operations and the scroll ring function. The Kensington web page also lists Chrome OS under Compatibility, so I was hopeful that there might be a Linux-compatible version of this utility. Alas, no such luck.
Finally, a few words about the price. I first saw this trackball on the Kensington web site sometime last summer. It had a price of $99. I immediately searched for it in Switzerland, and finally found it -- with a price of about CHF 215 (that's more than $200)! Yikes! I've been living in Switzerland for a long time, and I know there is a substantial markup here, but that is just completely ridiculous.
I kept checking for it periodically, and watched the price here go slowly down. It finally hit CHF 119.- two weeks ago and I ordered one. Since then I have seen it go below 110.- in a few places, so there is hope, even if you live in Switzerland...
The bottom line is that I really like this new trackball. I have had a lot of trackballs over the years, and this is one of the best that I have seen. I have already started using it in preference to the Logitech M570 trackball I have had on my desk for the past few years.
P.S. Don't read this unless you are interested in a very geeky explanation of the xmodmap command mentioned above.
The numbers given in the xmodmap command specify the mouse button functions, as follows:
Left mouse button
Middle mouse button
Right mouse button
Scroll up (or down, depending on how you interpret "natural scrolling")
Scroll down (or up, depending...)
The position of the items in the command specify the button to assign a function to. So the first parameter after the equal sign assigns to button 1, the second to button 2 and so on. So this means in the example command I gave above, I assigned function 8, "Back", to button 2, and function 9, "Forward" to button 8.
Of course, to do this mapping you have to know which button event is being produced by each button (or ring) on the trackball. That's pretty easy to figure our using xev - details left to the reader.
All clear? If so, then here's a small test - what would the command be to change the scroll ring to horizontal scrolling rather than vertical scrolling? Submit answers in the comments...