Flex and Cairngorm

I know that I am behind the times with Flex and this is a continual learning process, but I wanted to learn more about MVC structures and Flex. I chose to explore Cairngorm and found this site as a great launching pad for learning more:

http://www.davidtucker.net/category/cairngorm/

I am not sure how it compares to other frameworks like PureMVC or ARP (or any others), I just randomly chose Cairngorm to begin with, especially because David Tucker has great simple examples of usage.