i have the same one its pretty cool i got it from ebay and i use it for the games and as a primary mouse but once in a blue like it sticks a bit may bey needs a cleaning but its good for the price i just rechecked it on eBay and some one has it for a lesser price then what i paid which was about the same amount as that link you posted but this one is lesser may bey they have different colors too i have another one that's supposed to be here today hopefully because we have to much snow over here the other one is from x arcade.
http://www.ebay.com/itm/4-5-cm-of-Diameter-Round-Connector-PC-Trackball-mouse-for-arcade-machine-/281564888872?pt=LH_DefaultDomain_0&hash=item418e933f28