Does work on AoE spells, but MP recovery is capped at the spells initial cost. (Aja a large group of monsters and your mp remains the same after the nuke)
Assuming it works even on AoE spells, you could definitely gain back more MP than you spend by casting spells in Abyssea. With enough targets you can do it outside of Abyssea too of course. Personally, even for single targets in Abyssea I would've preferred to use this over slightly higher MAB.