If you have several sites that are nearly the same but different contents, then this is the extension to go for!
Ease of use
Difficult to use, but once setup it works at the touch of a button
Support was really excellent. I had a 500 error during the creation of the slave site and Edwin spent a 2 hours with me trying to solve it
Very exhaustive documentation
Value for money
Dont know it yet (too early to say) but it may really save a lot of time especially with regard to updating security etc...