Mastered Esper Icon

It's the only place where you can see MP costs for espers outside of battle, if I'm not mistaken. In LLGs, your MP is low enough that you equip espers based on who can afford them, so I wouldn't say nobody would miss it.

I guess you are right.  I always just looked at the MP usage in-battle and simply equipped espers based on which characters have learned the magic or not.  I suppose this can change based on the hack in question, though.