Well, I've just finished my first stamp using Mastercarve. Generally speaking, I don't think I would use it again. The material itself is far too spongy for my liking making it difficult to carve (the small parts move to get away from the blade).
Potential spoilers below (I may or may not be actually planting this carve; I don't think anyone will actually know what the carve is supposed to be.)
For your viewing pleasure, some badly taken pictures of the carve as well as the first stamp - all prior to be cleaning the image up: