Gaggle and Google Apps

Has anyone had much success using Gaggle's paid service for Google Apps?

http://www.gaggle.net/googleaps.html

I am interested in using gmail and having it filter through gaggle.net's filters, but have a few questions/concerns.

Can 1/2 my class be using the gmail portion and the other half just gaggle.net, but still easily share the same address book?

Does the in-school address book work at all with gmail when running through gaggle's filters?

Has any bought this for the whole school/district, and how do you like it? Any concerns?

Thank you,

Phil