Well, the Moon Cup is manufactured by the company that also makes the Keeper...I believe it has the same dimensions as the Keeper, just in silicone. The Mooncup UK is made by entirely another company, and it's different from other cups in that it's very short and has a thick rim.

This post (http://community.livejournal.com/menstrual_cups/473758.html) has comparative pictures...if you scroll down to the second-to-last-comment, there's one that's been edited to include the dimensions. :)