Yes, it takes an Ability slot, so unless you use the Bare, Mimic or Time Mage class, you won't be able cast five spells on a row, but you can still attack your enemies with 2x Holy, 2x Flare, 2x Bahamut or something like that. With a Time Mage and X-Magic, you can start a battle by casting Haste2 and Quick, then you just cast 2x Meteor twice. It gets even cheaper when you have a Mimic with X-Magic, Summon and Time Magic, so you can use X-Magic to cast Bahamut-Quick, then 2x Bahamut and Mime it. I think it's just right that you need to level up your jobs a lot to learn such a useful ability.