content: I was a previous user of the Logitech trackball mouse, which I found comfortable but did not like that took up a lot of precious real estate on my desk. It also required frequent cleaning of the contacts; eventually, the mouse was erratic as i may have bent the contacts when I cleaned them. When I saw this optical version, I ordered one for home and two for work. Since I am a long-term user, I love the thumb action, but the colleague I ordered the second one for at work couldn't get used to the track ball at the side. I am delighted. This mouse does just what an optical mouse should do - move about the screen without physically moving the whole unit.I was pleased that it takes up only slightly more space than a regular optical mouse (though the slope of my old space hog was still more comfortable!) I 'd say go for this prouduct!