You unlocked N!...? Are you sure that's not UV? I think N! requires an AoMr win [EDIT: corrected from "full win"] to have been done, but I'm not sure.
1 armor for 8 shots means 16% max HPs saved, assuming you're still at 50 max HPs. That's a huge difference, aspecially if you're shot at more than once. Anyway, consider that IM is a 20% increase from 50 HPs, so the match is at least close even at just one attack, but since use of those additional 10 HPs requires healing (often a full heal, otherwise you may stay beneath the 50 HP line), TaN is more likely to come in handy. On the other hand, if you're down to 2 HPs, are still in danger, have no access to healing and happen to level-up, IM can be a life-saver :)