It seems to be more free-form than PureMVC, to demand less boilerplate code and to make a greater use of Flex concepts like events and tags.
Having just tried two frameworks (Cairngorm and PureMVC), I will not look into Mate right away. But I plan to do it eventually.
Some reviews are very positive:
- Why and How I Switched From PureMVC to Mate
- Mate: Event driven framework for Flex
- Mate Flex Framework Alpha in Spotlight
- Mate: A Flex Framework for People who Hate Frameworks