Why do people want to max MP recovery?

Yes, but still, how does Oak Barrel work? is it basically Dark Sight with a chance to be hit, but you can still attack or something?

Because if it doesn't let you attack while using it, I probably won't get it.

I can go check for you, but I'm 80%(?) sure that it doesn't let you attack and "smart" (M.atk monsters?) monsters can tell if you're hidden. Pirate's version of Dark sight?