A few people have argued for the 'big shiny red button' I think having three ADR buttons, neatly out of the way is just fine. I think we all realise that this is not quite the way Airbus intended things however should the above sort of situation start to unfold then the PIC or their delegate would be well within their rights to switch off two ADR's as per the OEB, just don't switch off the IRU's by mistake!