I have had a trackball mouse in various configurations for many years. I bought this "Kensington Expert Mouse Trackball" just recently and gave it a try. The big attraction for me in making the purchase was the larger ball itself. The advantage of the larger ball is more precision control of small movements. Very valuable in detailed mouse manipulation type work. The ball size is 55mm or about 2.165 inches. Almost twice the size of a typical trackball type mouse. My view is that it worked perfectly, and I have absolutely no complaints. I really like the ball size for the reasons given above. And found the scroll ring an absolute convenience. I did however have a couple of reservations relative to my own personal tastes. Here they are:The overall size of the mouse platform is a bit massive. I have relatively large hands, but even so, the larger size of the overall mouse felt awkward.The ramp angle for me is a bit steep. That angle caused more bend in my wrist that was comfortable. The pad extension provided was not a help. It made the overall mouse experience bulkier.As one other reviewer remarked, I felt the button placement was slightly awkward. I could not comfortably reach the buttons and the trackball at the same time. I had to reposition my hand to adjust back and forth between those controls. On the plus side, I really did like the ball size and the scroll ring for detailed mouse work.If I were to take all that those ideas and offer a design improvement suggestion, here it is.Kensington should redesign their, "Kensington Orbit Trackball Mouse with Scroll Ring (K72337US)" utilizing the larger 55mm ball. And in doing so Kensington should redesign to maintain the overall size as close to the smaller K72337US size as is engineeringly possible. Utilize the larger 55mm ball size. Definitely retain the scroll ring and the button placement. Such a product would have great appeal, functionality, comfort, and the precision of the 55mm (2.165 inch) larger ball.All in all, I liked what was attempted in the "Expert Mouse" version with the larger trackball, But to be an ergonomically more pleasing tool, the "Expert Mouse Trackball" design needs a bit of tweaking.I've owned several Kensington trackballs over the years. I've own this same model before and used it until it died. I'm a professional audio, music, and video producer, so I use it regularly and they wear out quick for me.My issue with this model is that the buttons will sometimes release my click before I actually release the button. So if you do any work where holding down the button is a regular part of your workflow, I would not recommend it. On several occasions I've been doing editing tasks and the left click button releases, even though I'm still holding the button on the trackball. So files get dropped in the wrong place, wrong menu selections are made, etc. Pretty frustrating. I also do a lot of tutorial videos as part of my job, so this is even more frustrating when this happens in the middle of a video recording.I've also owned the Slimblade version, and while that one seemed to die out on me after a couple years of use, the trackball movement and button clicks were more accurate. I wish I had purchased the Slimblade version again, instead of this model. Save your money and pay a bit more for the Slimblade model.I work as an audio engineer with Pro Tools and once I was able to get comfortable with the track ball I couldn't live without it. You definitely have to stick with it though, the learning curve is strong. Some drawbacks are that the ball and underneath the ball get nasty pretty routinely, lots of oil and crud build up which makes the ball not move smoothly and also affects the sensor inside from picking up the motion. The other major downside so far is that I used this exact mouse til it died once, probably only used it for maybe 3 years or so. Also did the same thing with a wireless version of it which lasted even less time. Oh and the USB cable could longer for sure.I used trackballs of varying types all the time years ago and just got away from them with time as I was working mostly on the run with laptops. These days I'm fixed at my desk a lot more and decided after having a defective Logitech Hero that kept double clicking things that I'd try one of the Expert Mouse units again.Very solid build, modern level of resolution and the software allows for some nice customization of the mappings and button assignments.I have fairly large hands and find this more comfortable that a typical mouse. My hand doesn't cramp up as much.These track balls are best for "consuming" media or operating the controls of software applications, if you really need fine control a traditional mouse or better yet, a digitizer pen are better options. It does take a few days of adjustment if you have never used one. You will want to experiment with the acceleration and speed thresholds and the button modifier to go to high resolution, fine, slow mode is very handy too.The only thing to know and I already did from years ago is that you basically lift the ball out and clean the guide posts pretty much daily to keep them nice and smooth. I just use a dry napkin to wipe them off, nothing fancy. The ball rewards clean hands, it's not going to treat you well if you keep using it during a nice lunch of fried chicken.I own 7 of these for my company. Every machine has one. Space savings and more control, not to mention better for RSI. Love it!Tengo muchos años usando trackballs, usé dos modelos de Logitech uno para los dedos centrales (Trackman Marble) y otro para el pulgar (M570).El modelo de Kensignton es el más cómodo y preciso que he usado, la rueda giratoria para hacer scroll se siente totalmente natural y el tamaño de la bola permite hacer mucho movimiento con la mano para descansar, por ejemplo moviendo todo el brazo en lugar de sólo la muñeca.Los botones son configurables por medio de la aplicación de Kensignton lo que lo hace aún más versátil.Lo recomiento ampliamente (ya compré otro para mi hijo)Es muy incómodo para trabajar, es de orientación horizontal, y aunque puede ser ambidiestro, es cansado porque no es natural la posición de la mano, además los botones no tienen una posición ideal, tal vez para alguien que sea su primer trackball se puede habituar, en el mercado ya existen otras opciones más anatómicas. Lo compré porque ciertamente hace muchos años eran pioneros, novedosos, pero no me había tocado trabajar con ese modelo precisamente, se ve muy robusto, duradero, bien hecho, fuerte, pero le falta mejor diseño.Kensington es una de las mejores marcas de trackballs. Y el Expert es uno de los mejores trackball ambidiestro.Desde hace años use Kensington Orbit w/ scroll ring y también use durante un tiempo Logitech trackman marble, muy recomendados también.Un punto que no me gusto como primera impresion del Expert es que es muy lento (400 dpi), para mi que uso dos monitores. Sin embargo una vez que se configura la velocidad y aceleración del trackball se tiene buenos resultados. El diametro del trackball 55mm es de lo mejor comparado con el Orbit w/ scroll ring 40mm.Actualmente uso en mi mano izquierda el Orbit y en la derecha el Expert. El software KensingtonWorks reconoce muy bien los dos y trabajo con los dos al mismo tiempo sin problema.Otra recomendación personalicen su trackball desde KensingtonWorks, los botones pueden tener diferentes funcionalidades para cada aplicación. Por ejemplo para edición de documentos tengo configurado copiar y pegar, para navegar por internet tengo "back" y "home" (para ir al inicio de la página)Para dejar claro algunos puntos claros sobre un trackball de otros comentarios y nuevos usuarios.1) cada mano es diferente, diferente tamaño, dedos, etc2) cada problema de mano/muñeca es diferente3) cada persona es diferente, diferente postura, diferente escritorio, diferente altura.4) cada trackball son diferentes, uno no es mejor que otro. Tendrás que probar cual se adapta mejor a ti.Por ejemplo me gusta la altura/inclinacion del Expert (slimblade no lo tiene), pero probablemente el tamaño del trackball 55mm no sea cómodo para una mano pequeña y se adapte mejor usando uno de 40mm. Lo mismo aplica para la forma del trackball y la forma/tamaño de tu mano por ejemplo Kensington Expert y Logitech Trackman Marble muy diferentes en forma. Otra diferencia es el manejo del puntero con los dedos Trackman Marble que esta posicionando mas a la punta de los dedos que el Expert que esta mas centrado a palma de la mano.I have done a lot of ergonomics work for a major bank. Carpal tunnel syndrome or repetitive stress injury is a common problem for people who use a computer mouse extensively.The Kensington Expert Mouse is an excellent alternative that will help a lot. Depending on how bad your case is, you may find yourself using this alternative for a year or more.The problem arises in most people because they use the mouse incorrectly or it is too small for their hand. More on this later...The expert mouse is so effective because it decouples positioning from the click or selection process. You position the pointer with the center of the middle three fingers (fingers are not bent), THEN, you select the target by using the thumb to click a button. These are TWO separate actions. There is nothing to hold or squeeze.The correct way to use a mouse is to NOT grip or hold it, but to simply "ride" it with your open hand. The clicking operation should be done with a straight finger, not a bent one.In some operations, the Kensington Expert Mouse is quite handy because you can park the pointer in a specific position and it will stay there.One of the unique features of this Expert Mouse is the 55mm size of the ball - about the size of a pool ball. . Devices with smaller balls will be much less effective. Another is the positioning in the middle of a cradle that allows you to use your flat fingers, not your thumb. If you periodically clean the expert mouse, it will last many years. There is virtually nothing to wear out.I’m using it in my DAW, Studio One with dual monitors. Even after just a few hours’ use my workflow has noticeably sped up. Compared to a normal mouse, moving between monitors is super fast and placing the cursor more easily accurate. I’ve set the unit up with top left and top right buttons as left/right click and drag. The left drag button really speeds up setting automation curves. The bottom 2 buttons are set as double click which again speeds up work in the DAW.I’ve experienced some oddities: At times for some reason the clicks are slow to be read. Also, while the double click setup works great in the DAW, it doesn’t work that well on the desktop, where a normal double click works much better.All in all, very happy with the product. I should have switched to a trackball years ago.