Post Big Bang Holy Arrow question.

MP Eater did get dramatically nerfed in restructuring. I think it was changed to 20% proc rate to recover 10% of the monster's MP at max. It's hard to say how useful it is now, though, if it triggers with each strike (like Ice Strike, Thunder Spear, Big Bang, etc), it might be a bit more useful.

Mind you, it's still much more useful than MP eater now, just because monster's max MP is so much higher. Regular mob MPs right now barely get to 200; post-BB, i think they get up to 1000 by the mid third job. I read a post on the forum that while training, this person only used two MP pots per level. That saves a ton of money, especially compared to the current millions that at least I needed to level with ultimates.