If we look at the modules with all skills level V and no ship bonuses, we see that they are pretty much the same in terms of fitting (tech II actually a little more at 6MW and 6 tf compared to 5 and 5 for the AAR) and we get this result:
Small Armour Repairer II - HP Repaired = 80 (88 overheated) HP
Small Ancillary Armour Repairer I - No Charges = 45 (49.5) HP
Small Ancillary Armour Repairer I - Nanite Repair Paste = 135 (149) HP
In other words, for 36 seconds the tanking ability of the AAR is over 50% better than the Tech II version for the same cost in capacitor and less fitting. This pattern is the same for medium except the amount of time it boosts better is 72 seconds, and large is ~90 seconds.
Much truck was also made about the module being limited to one per ship and, yes, this doth suck. BUt that does not mean that dual rep and triple rep ships cannot have one of the reppers being an ancillary version to increase the short term tank even more.
Ultimately I see this module as being perfect for brawling ships looking to cause as much damage as possible in the shortest amount of time at the start of a fight and I plan to modify my Dual Rep Incursus to include one like so: