When I was flying in States I flew with some captains who were FFDO. Honestly, most of the first officers hated flying with FFDO. Not because they were pain to fly with, but becauseof the fact that we had to take extra steps everytime we opened the cockpit door. Before we could let anyone in the cockpit he'd have to put the gun away and lock it. Too much work just to go and take a piss. So we tried to avoid the FFDO's.
I guess it is a good programme, but than again, never heard an FFDO using his/her authority.