Pros: Smooth, accurate tracking
Comfortable angle
It works. I take for granted the measure of control I expect, until I do not have it. How long it works without problems will tell me about its build quality.

Cons: Small complaints:
- No Scroll wheel click.
- The scroll wheel does not move smoothly. It does not have the ratchet of a normal scroll wheel, more of a rubbing/grinding.
Only major problem:
This is not your standard mouse, you will have to train your fingers. I have been using it at work (8+ hours a day) for over a month and I am still trying to get used to it. My last trackball had the same layout as a mouse (index finger for left click, ring finger for right click, with a clickable wheel in between). However with the trackball in the center, I have to use my thumb for left click, my index finger to move the trackball, my ring finger to scroll and the next finger for right click. There is also no set way to position the trackball, so I have to carefully adjust the its position so my fingers fall on the buttons. I feel like I am trying to type with my nose.

Other Thoughts: I bought this trackball because of its reported quality construction. So far it seems to be well built and functional. However, if I am not
able to overcome 30+ years of mouse conditioning, then build quality alone is not enough.

Pros: the scroll ring took less than five minutes to adjust to, its amazing. comfort pad is kindof nice. good for casual computer scrolling and clicking.

Cons: the angle is wayyyy too steep, I have to pitch my wrist at such an awkward angle to operate the overly large ball. Since the wheel is so large, it is not nearly easy to control as a more nimble smaller one. I often find my myself pushing the ball with my finger, rather than rotating, to get the desired amount of spins needed to move the mouse from one part of the screen to another, resulting in choppy movement. Most awkward thing in the world is trying to hold a button pressed down and operating the ball, especially the right button. Multiple click on the left click seem to tire out a weird tendon in my hand and makes me weary to continue using this mouse for high operation. the comfort bad is extremely difficult to remove without accidentally breaking the very skinny pegs. Biggest problem with this mouse is there is no where to press the weight of your hand on your mouse. allowing you to get the steady control to operate a tracking ball, I have to lift my hand off the desk slightly to really be able to turn the massive ball

Other Thoughts: I have a large palm and avg length fingers, I have decided to return it today, however I can not since I have owned it too long. So I might end up shaving off some of the rear to reduce the sharp angle. I think if the angle were a lot flatter it would allow easier effort to push the buttons and control the track bar. unfortunately since both pegs broke on the comfort bad I might drill out where they used to be and crazy glue a tiny bolt to replace the OEM 'pegs'

Pros: Precise in a way that no normal mouse ever can be. Smooth and precise scroll wheel. Very high quality, I have been using the same trackball since 2010.
Much less stress on your hand than a normal mouse.

Cons: Requires frequent cleaning, it even needs to be taken apart from time to time to keep it clean.

Other Thoughts: I have been using Kensington Expert trackballs since 1991 and as long as they keep making them, I will keep buying them.

Pros: I used the basic orbit for the past many years, and only ordered this because the buttons finally wore out, using this is a blast compared to it with the added four buttons being remarkably handy and the scroll ring allowing me to play the games I couldn't previously due to the orbit grey's lack of third mouse button and scroll ring. it's simple plug and play without any need to download the "trackball works" software, which is convinient, and it's design is surprisingly manageable after some practice.

Cons: I found it awkward using at first due to it's design choice, and after reading a review stating the cushion it comes with for the wrist was rather bad I see why now, it attatches with two pegs that hook beneath the mouse, the pad isn't quite properly molded and leaves a weird gap, deciding to take it off after noting this weird gap I found it was a struggle to budge it, and in doing so bent the prongs out of shape nearly garunteeing it won't fit again. the scroll ring does feel a tad gritty like some of the parts keep catching, but it's only during large rotations that it's really noted. and aside from that the buttons can be kind of stiff, requiring some pressure to activate, but I assume most of that will wear out given time.

Other Thoughts: Overall for the 60 ish bucks I spent on it, I say it's a pretty decent mouse, it's ready straight out of the box, it does all it needs to, and works perfectly with the programs I've needed it for, so overall despite some quirks I'm content with my purchase and suggest considering the mouse, or trying one before knocking it.

Pros: Bought in December 2007 and it still works well.

Cons: The scroll wheel movement always felt a little gritty; I just got used to it.

Other Thoughts: I use a gel pad with integrated wrist rest; it's more comfortable than what comes with.

Pros: I've been using one of these for over ten years - yes, the same one! They are built like a tank, and once you get used to one, you will NEVER use a mouse again. This is simply the best pointing device ever made, period.

Cons: Expensive - but you get what you pay for.

Pros: -Symmetrical trackball WITH A SCROLL WHEEL! Logitech, please take note.
-Firmware that allows for simultaneous clicking to add further functionality, ala middle click and 6th click. The firmware is good enough give you lots of options here.
-Could probably kill someone with it if I needed to defend myself against an intruder.

Cons: -Massive. I have small hands, and I could not find a comfortable way to rest my hand on this mouse to be able to reach all four buttons.
-The button layout, and I had a feeling this would be the case, is not economical what so ever. It simply was not designed for the top buttons to be reachable with the hand in a resting position.
-The buttons are too heavy to click, and especially to hold.
-The wristpad is laughably bad. Too firm, never tested for actual use and as such misshaped. The plastic thing that was suppose to connect the wristpad to the mouse is one-time use, and promptly broke to pieces upon trying to take the wrist pad off.

Other Thoughts: No, ergonomics was not a goal set in mind when Kensington made this mouse. I'm not sure what goals they actually set because it's almost unwieldy. I'm coming to the Expect Mouse from Logitech's Trackman Marble, which is far from ideal itself, but it has ergonomics on its side, and moving from that to this is not pleasant. With the included wristpad my hand rested heavily on an uncomfortable part of my wrist. With a third party bead wrist pad I'm in the same boat as any normal mouse except my fingers are stretched out everywhere in order to reach the buttons, and that starts to wear down on you. I was hoping to rest my palm on the mouse (the way I do on the Logitech Trackman) but that was no the case here, and that's the biggest issue I have with this mouse.

Pros: Very good quality, works well, solved my carpal tunnel syndrome.

Cons: Gets dirty quickly, have to clean it often.
Expensive for wired USB.
Would have expected wireless for that price

Pros: reduces carpal tunnel issues, because it's stationary

Cons: trackball is not secure, can fall out and roll anywhere. scrolling has a gritty feel to it, not what you expect from a high priced mouse. the worst problem for me is the top 2 buttons have to be programmed, but they will stop working. also, you cant use a top button with a bottom button. you have to use either the top 2 or the bottom 2. the scrolling worked briefly, then failed in the program i use. the clicking often fails me, i have to double or triple click to get it to register.

Other Thoughts: no drivers included, you have to download it and run the program in background. the ergonomics are bad for me, i have to use my index finger to roll the mouse. very imprecise for what i do.

Pros: I've been using this brand of trackballs for 10 yrs and this one is the best. I own 4 of this model and use them daily. I do not lay my palm over the ball I just lay the three middle fingers over the ball and only use upper buttons for special purposes. It seems some are trying to access all buttons from one position of the hand. 7 possible functions are available beyond the mouse movement itself. 4 buttons, 2 chording commands and the scroll ring, which is directional as to your preference. I had to use other software - freeware- until Kensington came out with the new software, and it works great with 64bit Vista and Win7, I haven't tried 8 so can't comment. This model is much improved over the last

Cons: 2 cons on these. 1 - is the scroll ring quit working on my oldest unit. 2 - scroll ring is a little on the inconsistent side as far as firmness and feel - between the 4 units I have, as in smoothness comparing one to the other. And I do feel the first unit I had was the worst scroll ring feel out of the box, and the newest, was the best feel. So maybe they got the problem corrected. In all honesty, the scroll ring that failed was very old before it just recently failed. But all other functions still work.