Great ... once you get used to it
Basically it's very comfortable to use but after years using ordinary mice it takes some getting used to, and not just because your hand stays still rather than moving as normal.. Firstly, the trackball movement is VERY light, it takes some practice to get used to the tiny thumb movements that move the pointer, but once you are used to it you can get both fast large movements and delicate ones.
The slightly bigger issue is the placement of the two page forward and back buttons (the functional ones, not the usual right and left click) and the scroll wheel. On a normal mouse the two buttons tend to be on the side and worked with your thumb, fine, it's often all your thumb has to do after all, but with your thumb working the trackball those buttons have to be worked with your index finger, which is OK as they are well placed for that. But then which finger is best to work the scroll wheel? The index finger would be usual but that gives it an awful lot to do, so I find I swither and sway a bit between using my index finger and my middle finger on the scroll wheel. Still having to get used to that.
Finally, the ergonomic angles are great, much more comfortable than with an ordinary flat mouse, but a better ergonomic conventional mouse would give some of the advantage there as well, but fair's fair, it is comfortable in the hand ... so long as your hand isn't too big. If you have very large or small hands you may struggle, it's designed and sized for 'normal' sized hands. If you're more than a couple of sizes away from a size 7 glove you might find it a bit uncomfortable. And don't forget, it's useless if you're a lefty, it's strictly for your right hand only.
The only other point I find interesting is that I tend to find myself doing less on the keyboard with my right hand and more with my left as with the right hand set on the mouse and settled in it's better to keep it there.
So if it fits, and you're willing to put the time in to get used to it, absolutely worth trying, I consider it a definite keeper. Combined with a space mouse, CAD is transformed.
Verified purchase: YesCondition: New