It's still a question of whether or not the upkeep of the Crisis Arm is worth it. Robo, being your main healer, would be the one devoting himself his own healing, which slaughters his damage output against either multiple or counter-attacking enemies, and even if you start draining your items, or bring along another healer, then your just slowing down someone else. Plus, Armageddon Arm is all purpose, it works through defenses, barriers, everything, there is no enemy (aside from Spekkio, Shadow, etc.) that it is not a viable tactic for. If only for it's low maintenance and versatility, I still give my vote for the Armageddon Arm.