Here is my experience with the Trackman Wheel...
As a design engineer, for years I had problems doing CAD work. My fingers and hand would constantly cramp up after working long hours on the computer. I tried a COUNTLESS number of mice, trying to find one that would alleviate the pain and cramping. Then I found the TrackMan Wheel. Alas, SWEET RELIEF!! I didn't have that problem anymore. My guess is that because pointer movement is controlled by your thumb instead of your index/middle finger and wrist, it greatly reduces strain on those muscles. Whatever the scientific explanation, it WORKS! The shape is perfect, the performance is great, the control is smooth. It ROCKS! I now have one at my workstation at work, and one at home.
I wrote that as feedback many years ago. To this today all of it still holds true. This is a great mouse/trackball. I did have one incident where I had some upper hand/knuckle pain for about a week, but I was working more intensely than usual, and it's been the only pain I've experienced in over 6 years of using the device.
As many have mentioned there are a few things that would be nice to see as an update to this great design, namely a hyper-fast scrolling wheel, higher dpi trackball with better precision, a true cordless version with, and a few more buttons for usability/productivity.
Also, as others have mentioned, if the trackball starts to not glide as smoothly as it used to, all you need to do is pop out the ball, clean the contact points, and you're back in business. Some of the later revisions seem to use smoother/better materials for the ball contacts to keep it gliding as smooth as new.
All in all, it's been a great purchase. It really is that good.
Technical Expertise: Tech Savvy
I've used this product: More than a year