I currently own two explorers, one optical and one wheelmouse optical mouse. All three are different. The explorer (the dark grey one) has a total of 5 buttons (r-click, l-click, wheel-click, and two extra programmable buttons where your thumbs rest). The thumb buttons are very conveniently placed making it great for games. The explorer is also modeled in a way that takes a little getting used to and I hear that people with small hands find it quite uncomfortable. The optical (the one Amazon.com is selling) also has 5 buttons except that the extra two buttons that were nicely located by the thumb in the explorer has been split to one on each side of the mouse which makes one of the buttons closest to your pinky a little out of the way and not as easy to get at (not good for gamers). The optical is also we suited for ambidextrous or left handed people I have heard no complaints on the feel of this mouse, it is quite comfortable. The optical wheelmouse LOOKS like the optical except that it has NO EXTRA BUTTONS! Just r-click, l-click, and wheel-click. The sides are colored grey like the optical but it's just for fashion. This mouse is also quite comfortable for any hands. I would say that the mice would go to these certain people:
Explorer Mouse - Gamer/Hardcore Gamer
Optical Mouse - Casual Gamer, Heavy Internet Use
Wheelmouse Optical Mouse - Business Use, Casual Internet