Currently it works in a way that once you turned it on, it increases max amount of HP you can have, without actual adding those HP. That means that for this module apply it's effect, you need to armor rep those HP, or ask someone to RR you. As an opposite to, says, Speed Nexus, or Ewar Nexus, or whatever, the effect of Armor Nexus is kinda delayed or even not applied at all - during the battle, one who receiving that bonus, can be simply unable to get that extra armor, because he is either doesn't have spare energy to run a cycle or two (expecially with those new changes), or have their less than 100% - Armor Repair income (which means, they wouldn't feel any difference), or even too busy shooring or running to see if they are under effect.

Taking all that into account, I hardly doubt anyone does use Armor Nexus, and probably never will.

I suppose that Armor Nexus should increase / decrease both max HP and current HP.