It's perhaps the only spell/song in EverQuest that actually gets worse as you level up. It actually works less and less the higher level you are. It will be fully replaced by the level 28 mez song Crission's Pixie Strike. I confess I haven't tested the AE mez one much, because as soon as I got the single-target one, I greatly preferred using it.
Only-having-AE-mez sucks. You mez everything and then the group attacks one mob and of course it goes for you because mez spells are high aggro. You take damage before the tank can get it off you. Then, in order to keep the other mobs mezzed, you sing the AE mez song again. That also re-mezzes the current target, which is being hit, so the mez is instantly broken and now it hates you again. It goes back to hitting you. The mob finally dies. Then the group breaks your next mez, but you've mezzed that one even more.
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I guess if you're tanking anyway, and/or if the mobs aren't wrecking you due to relative level or good gear, it's fine.
Single-target mez is far more usable. You can continue to twist in other songs if you're only mezzing one or two. You can also leave your mez running on one mob while meleeing a different mob. If you're feeling like playing with BOTH hands, you can melee Mob B a bit, target mob A and hit it with a mez, then start twisting other songs, target Mob B and resume meleeing...you get the idea.