Advanced Iframe simply does things that other iframe plugins (or the default iframe function) cannot do. If you need more functionality than simply inserting one static page into another, i can absolutely recommend this plugin.
I also thought the support from the plugin author went way beyond anything you would expect from a free plugin (to the point that i would say that i received lesser support on many paid plugins).
To eleborate on this; I needed a function that was not present in any of the existing iframe plugins. I set out the support questions both here and with "that other big iframe plugin". Within a week Michael had recoded his plugin four times to enable my wanted function, while i have yet to receive a simple answer on the other thread.
To put it briefly; If you need a robust i-frame plugin with lots of functions and excelent support, look no futher; Advanced Iframe is what you will want to use.