Luc47,
Vilas answered question 1 pretty comprehensively as he is apt to do. Can you give us the reference for your second question, I am not aware of such a restriction.
Having -FD2 or 1FD- is a recipe for a disaster such as this:
https://en.m.wikipedia.org/wiki/Indi...nes_Flight_605 (and other alpha floor incidents world wide to say the least)
But it would appear that that is not your question. There is no such recommendation in my manuals that are very much aligned with Airbus.
Perhaps what you have there is simply a recommendation as to how your company would like you to practice your hand flying should you wish to do so, but that would certainly not be an Airbus standard requirement.