Which is "better" (loaded question, i know)?

First, here's what the admin section does
  • Handles committee finances
  • attendance records
  • user profiles
  • CMS for public pages (basic text and images)
  • adds news to articles
  • possibly maintain google-like calendar
  • maintains documents for committees and elected positions


1)
The admin section is delivered as usual, via HTML built by php/mysql. With my moderate experience in javascript, some transitions made ajaxified, but most things requiring a page refresh

2)
The admin section is delivered as a RIA built in flex (flash). service calls to ZendAMF(php/mysql) mean no page refresh, and everything looks and feels like a program, not html page. Users will have to be trained to NOT hit the back button, otherwise having to reload the program again.

This will ultimately be repackaged for various non-profit type groups I have lined up. Are there major drawbacks that are obvious to you enough that I should pick one implementation over the other? (Besides, of course, flex's asinine RichTextEditor). Hypothetically, which would you prefer?