Papa...Damn good question...I myself will be using the FDC for my last claim of I.U. However, whatever the answer, I would highly recommend you get ALL your ducks in a row b-4 you do anything. My understanding is, if you forget ONE thing, then it turns into a regular filing and we know how long that takes!
And most def. SEND IT CERTIFIED MAIL! Reason is, on line you cannot present your evidence therefore again, causing delay.
And yes, it is for all Veterans, not just AO. If you are AO than proceed with it. This FDC is fairly new...not even my VSO knew about it until I brought it to his attention. Lastly, you can check the VA web site to explain more. Best of Luck Papa