Rating: 
Summary: One of the better ones
Review: A great and reliable performer. Original models had troubles with switches. My current unit is about 5 years old and still working well. Ball and rollers require infrequent cleaning.
Rating:
Summary: Worth every penny- I have no pain now!
Review: Being 24 years old, I became very concerned when all of a sudden my back started having pains and my wrist started to hurt. I work behind a computer all day and it seems that regular mice, (especially the ones with the scrolling feature), were starting to cause pain. My employer was kind enough to supply me with this item to try to see if it alleviated any of the pain. To my surprise, I am so much quicker with my work and without any pain! I love this mouse! Your hand stays in the same position the whole time rather than moving around.. which can cause you to strain muscles in your back and/or lock your wrist. I am now ordering one for my home use and I would encourage anyone else that has back pain from working being the monitor too long, to give this a try!
Rating: 
Summary: Almost perfect
Review: I bought one of these about 2 years ago after reading many positive reviews, including PC Magazine, Jim Seymour, etc. and I have been very satisfied. My only 2 improvement areas are:a. The connector to the trackball body tends to unplug very easily. The connecting cord itself is rather short.
b. No USB connection, must use the included serial\mouse adapter.
c. No scroll wheel; you can use the auto scroll feature but in some programs tends to be skimpy, i.e. in WordPerfect and you have to shift settings to avoid it. Most of the programs or web pages offer no problem about it whatsoever. Pros: a. Extremely smooth, precise and easy movement and comfort, not once my cursor has stuck. Optical sensors read the stainless steel rollers (on ball bearings) movement, these rollers are really "the highest quality and smoothest movement available" like the legend in the box said.
b. Cleaning it is a snap, take the ball out, blow into the emty cavity, put it back, done.
c. Very sturdy, I know these balls are not built for falling to the floor, but sometimes your toddler takes it out of its socket and in the process could bounce before you react; mine had one or two hits on hard floor, and it got no scratch at all. The body of the trackball on the other hand, had a piece of a marble tile fall from a wall and had only a minor scratch. Most of the cons are fixed in the pro model with scroll wheel, without cord and some bells and whistles, but is a more expensive option, if you can live with these minor imperfections and want a sturdy, reliable performer you'll be a happy user.
Rating:
Summary: One of the best!
Review: i love the fact that it has 4 buttons and you can program "button chords" to do stuff. eg. if you press the top two buttons, the current window will minimize. it offers a lot of useful shortcuts allowing you easier access to the taskbar, cut/paste, common keystrokes or your own list of favourite applications. on the downside is the trackball shape; it is not made with the shape of your hand in mind as it is curved up at end so you can't relax your fingers properly. also, the NT support isn't up to snuff. i demolished my system when i installed a new driver overtop of the old one (take it from me - make sure you UNINSTALL the old one first!) the technical support people were not helpful or sympathetic with my plight so you may notice some lingering bitterness in this review.
Rating: 
Summary: good idea - needs improvement
Review: i love the fact that it has 4 buttons and you can program "button chords" to do stuff. eg. if you press the top two buttons, the current window will minimize. it offers a lot of useful shortcuts allowing you easier access to the taskbar, cut/paste, common keystrokes or your own list of favourite applications. on the downside is the trackball shape; it is not made with the shape of your hand in mind as it is curved up at end so you can't relax your fingers properly. also, the NT support isn't up to snuff. i demolished my system when i installed a new driver overtop of the old one (take it from me - make sure you UNINSTALL the old one first!) the technical support people were not helpful or sympathetic with my plight so you may notice some lingering bitterness in this review.
Rating:
Summary: Excellent
Review: I own three of these - one for each computer I regularly use. They last forever, and never even need cleaning as they never get jumpy. There is never any slippage, so it works much better than a ball-based mouse for things like Quake where you may want to make fast but precise movements. There are four buttons which can be programmed to do whatever you want. For example, I set one of the extra buttons to be the back button in my web browser. Now I can move through web sites one-handed without having to move the pointed up over the back button constantly. This also allowed me to switch my IE toolbar to use small icons with no text labels, freeing up screen space. The only possible suggestion I can come up with is that it would be nice if they added on a scroll-wheel like all the new mice seem to have. I'll never go back to using regular mice as long as Kensington keeps making these.
Rating:
Summary: Excellent
Review: I own three of these - one for each computer I regularly use. They last forever, and never even need cleaning as they never get jumpy. There is never any slippage, so it works much better than a ball-based mouse for things like Quake where you may want to make fast but precise movements. There are four buttons which can be programmed to do whatever you want. For example, I set one of the extra buttons to be the back button in my web browser. Now I can move through web sites one-handed without having to move the pointed up over the back button constantly. This also allowed me to switch my IE toolbar to use small icons with no text labels, freeing up screen space. The only possible suggestion I can come up with is that it would be nice if they added on a scroll-wheel like all the new mice seem to have. I'll never go back to using regular mice as long as Kensington keeps making these.
Rating:
Summary: Great Product
Review: Kensington 5.0 Expert 4 Button Trackball is a great product for any computer user, being extremely rugged, precise and versatile. It's especially good if you have hand problems like I do. A few years back I broke my neck and as a result experienced serious loss of motor control in my hands. Since I use my computer several hours a day, use of a regular mouse became more and more of a difficulty for me. I looked at the options and decided to try the Kensington Expert Trackball. I use it in an unusual way--I tie it to my chair, and use it between my legs. I used epoxy to glue a ring on the plastic bottom of the mouse's case, to which I attach a nylon cord which is tied to my computer chair. This was the answer to my troubles, as I am now able to keep my wrists and arms almost straight when using the mouse. It is a very secure and ergonomic way to use this product. The product itself definitely rates five big stars for quality and durability. This product is a must-have computer tool, for me at least. I predict you'll especially like the "Easy-Launch" feature which enables you to program all kinds of functions onto the mouse.
Rating:
Summary: Great product if you have hand problems
Review: Kensington 5.0 Expert 4 Button Trackball is a great product for any computer user, being extremely rugged, precise and versatile. It's especially good if you have hand problems like I do. A few years back I broke my neck and as a result experienced serious loss of motor control in my hands. Since I use my computer several hours a day, use of a regular mouse became more and more of a difficulty for me. I looked at the options and decided to try the Kensington Expert Trackball. I use it in an unusual way--I tie it to my chair, and use it between my legs. I used epoxy to glue a ring on the plastic bottom of the mouse's case, to which I attach a nylon cord which is tied to my computer chair. This was the answer to my troubles, as I am now able to keep my wrists and arms almost straight when using the mouse. It is a very secure and ergonomic way to use this product. The product itself definitely rates five big stars for quality and durability. This product is a must-have computer tool, for me at least. I predict you'll especially like the "Easy-Launch" feature which enables you to program all kinds of functions onto the mouse.
Rating:
Summary: Great Design, Poor Software
Review: This is an excellent trackball. I have used it for some time now, and until I picked up a MS Trackball Explorer, this was my favorite input device. While I enjoy some of the "advanced" features of the Trackball Explorer, such as optical sensors (no cleaning!), scroll wheel, and ergonomic shape (this is a great piece for web surfing), the Expert Mouse still has a special place in my heart. :) For longer periods of use I generally prefer it, and the large ball makes my hands happy. Also, tech support is PHENOMENAL, far better than MS. In fact, I had to replace my expert mouse not long ago (5 yr warranty!) and they happily sent me out a new one. No RMA, no return, no _anything_ except "we'll send one right out". And they answered immediately. Most of the time with computer tech support, I don't even bother, and either try to fix it myself (easier said than done w/ hardware) or just bite the bullet and replace it. In this case, it was a pleasure to call. If I could give an add'l star for "extra credit", this trackball would rate a "6".
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