Very good comfortable mouse with a nice scroll wheel for scrolling. For those who often use the middle click for dragging in graphical environments, I don't think it will suit you... You will need to install the Kensington software to accept middle click by pressing both buttons (right+left) simultaneously.

I give it 5/5 stars because it is the most ergonomic and comfortable mouse I have ever had and the only one I have been using for the past ten years or so. With regular mice, my fingers start hurting after a few days. This particular one is the fourth one I have bought, as due to my long daily work hours, the left click button wears out every two years or so. That is its only downside, as otherwise, it is the perfect mouse (for me), as it does not strain my wrist or fingers.

Very good. You get used to it in 3-4 days. I've been using it for over 1 1/2 years. Super comfortable. Only some issues with overuse of the right click (it became loose and needed maintenance)

I have gone through Marble Mouse and TrackMan Wheel, both from Logitech, and now I am looking for something new because the TrackMan has worn out over the years...
My brother got this Kensington and I borrowed it for a week to try it out, but I can't say I was satisfied. Cheap construction and a plasticky feel, especially when it comes to the scroll ring and the two buttons.
Maybe if someone gets it as their first trackball, it might work for them (my brother is satisfied), but not for someone who has experience and wants a more sturdy, high-quality trackball. It is a lower-quality Marble Mouse with a "scroll wheel".

After a year of use, I can say that I am completely satisfied.

Its performance has not decreased at all, with a very fast response.

It is convenient, fast, comfortable, and above all ergonomic.

Its great advantage is the presence of the ring that replaces the mouse wheel.

I have tried it without any problems, on Windows 7 and Ubuntu Linux.

Once you get used to it, you will wonder how you worked for so long with the mouse and unnecessarily strained your wrist.

The only negatives I can think of are that its appearance may not appeal to everyone and that it may not be suitable for those who want a large ball size. Perhaps someone with special abilities may find it difficult.

I highly recommend it.