Pros: Incredibly durable, easy to clean, easy on the wrists, an absolute workhorse.

Cons: It does get linty fairly often, although it's easy to clean out.
No scroll wheel/middle button. If you use those, then this isn't your thing.

Other Thoughts: I can't remember when I bought this thing, but it's been years, and I've taken it around the world with me. It's amazing. It's never failed. Once you get used to the slightly different button placement, you'll never go back. I've never had wrist problems with it, even after hours of constant use. I can't recommend this thing enough.

Pros: This really is a great mouse! I used this for many years, even for gaming! I finally switched to a gaming mouse for more buttons and a scroll wheel, but I often miss my trackball for saving space on my desk. This mouse operates smoothly, is easy to clean, and functions well all around. I highly recommend this product.

Cons: None really so long as you understand exactly what you are buying.

Other Thoughts: Saw a con that said it has no scroll--this is easily seen in the picture, no need to list this as a con, although I do miss the scroll.
Also saw several cons that mention the third and fourth smaller buttons are hard to get to. This is bogus. Your thumb easily moves up to click the button above as does either the ring finger move up or the middle finger move down to click the other button.
One review talked about the ball easily falling out. What?! Not sure what you have done to your mouse to have this happen. If you turn the mouse upside down and shake it or if you are trying to use it upside down, then you might have this problem. Otherwise, you should be fine.
Finally, I saw another review mentioning that there is no wireless version...It's a trackball...it sits in a fixed position on your desk...why would you want a wireless version. "So I can sit across the room and still use my trackball?" Really? A trackball is designed not to be moved: therefore, there really is no reason to need a wireless version that you would have to charge and risk getting moved off your desk (etc.)
Understand when buying that this is a trackball mouse that is wired and has no scroll and only four buttons. You buy this for a well-priced, space-saving mouse that functions very well.

Pros: I have been using this mouse for more then 4 years and it is still very responsive. Usually the ball on the mouse would not roll smoothly after as much use as I have put on this one. It's long design fits my hand very well. Good support for the inside of my palm

Cons: Limited Features and the two secondary buttons are not placed well.

Other Thoughts: I'm a big fan of trackball mice and have owned a few different models and this one is a very solid option if you don't want to dish out a lot of money for the high end ones.

Pros: Smooth ball operation
Long lasting buttons
Comfortable design

Cons: None

Pros: Works well. Easy to clean. Very accurate.

Cons: None.

Other Thoughts: Allowed me to transition to a stand up desk. Used to use a keyboard touchpad. Now I rely on the Marble. If it gets slow or sticky, I pop it out and rub it on my shirt and then when I pop it back in, it glides real smooth. Its got lots of features but I just use the basics.

Pros: Having fairly large hands, it still feels quite fitting. If you have really large hands, this one might not be fore you. Software is very useful and buttons can be programmed to do anything you want. The best thing this does is force your wrist not to lay flat, but more into a (near) handshake position. I would say that is the main culprit for those that get problems with their right hand when using a regular mouse.

Cons: No scrollwheel, of-course knew that when buying. Wish the scroll ball was somewhat larger for more precision. Small buttons are hard to get to.

Other Thoughts: Have not used a regular mouse in over 10 years. First logitech trackball I had was a Marble FX Optical Wireless, unfortunately they don't make those anymore. Having used a trckpad for a couple of years, I get cramped fingers and was ready for a trackball again. This logitech one was the one that came closest to my first trackball. It's day 1 of testing, see where this goes.

Pros: I have used one of these for some time. They are positive and very dependable.
Combine that simple dependability with a reasonable price and you have a winner.

In addition, I work on a lot of computers for elderly people. Periodically I discover someone having issues with a mouse due to hand shaking or some other neurological problem causes their accuracy and mouse button clicking to be off., replacing the mouse with one of these trackballs normally cures their problem.

I have had several elderly clients thank me for getting them this trackball. It can be a huge asset to the elderly especially.

Cons: none that I have found.

Pros: Track ball is in the center and has 4 buttons.

Cons: Has no wheel, buttons on the right side are not in a comfortable place.

Other Thoughts: Bought this for a laptop gaming computer. I have a microsoft trackball with 4 buttons and a wheel on my PC so I wanted to get one that is similar in design as they don't make my model anymore. The Logitech is ok but I really miss the wheel and it is not as ergonomic as my microsoft trackball. Also having a hard time trying to figure out how to program the buttons but this is my first windows 8.1 experience so hopefully will find it later. Was the only trackball mouse I saw with the center ball and 4 buttons.

Pros: -Ergonomic. I have wrist problems and I can just rest my palm on this thing, it's shaped perfect for it.

Cons: -Button 4 and 5 placement... Not ergonomic. You can maybe hit the one with your thumb, uncomfortably, but the other requires some gymnastics. Should be towards the bottom front. Did anyone in Logitech actually ever try clicking those buttons because I'm guessing no.
-No scroll wheel. And let me just go ahead and get this out of the way: "universal scroll" ala SetPoint firmware is utter bullcrap and Logitech should know this.
-Trackman Marble hasn't changed in over a decade. I've had a version of this mouse back when it only had two buttons. They added 4 and 5 but put them in the wrong place, and never bothered to give it scrolling. Look for Kensington Slimblade for your answer, you can spin its ball across the Z axis for scrolling. Get with the times Logitech.
-SetPoint firmware is absolute trash and amazingly useless. It looks like it hasn't been updated since the mouse itself got updated. Again I reiterate, universal scroll is not the answer. Not to mention, scrolling with the ball is laggy and imprecise.

Other Thoughts: Give it a proper hardware scrolling option and move buttons 4 and 5 to a better location and I will rebuy the mouse in an instant and give it a 5/5 (improve the firmware to let me simultaneous click and I'll find a way to add a 6th star). It's 2014, these shouldn't be problems.

Pros: It just works. I have no idea how many of these I've purchased. I support multiple machines and all are equipped with the Trackman. I lend them to friends and never get them back.

Cons: None

Other Thoughts: Don't eat salted peanuts in the shell while using this mouse. The dust soon makes it very difficult to roll the ball. Five seconds with a tissue and you're good to go though. Can't speak for other mice.