1 is more efficient, but not generally to the point you wouldn't use 2. There's a few times I've used it, since it's on my bar anyway for easy swapping if I get level synched out of II. Generally if I'm solo and I went to gravity happy. But you'd probably never need to worry about it in a group since if you start to run low on mp and your luminous aethermajig isn't up you just hold off on attacking altogether.