I tend to use Mana Vortex for Tog in raid to unload on him with a +12 weapon. Doing so usually gets him down to about 120 bars before orbs spawn, and ensures that I have enough skills to use against Nerbe. That’s a very specific example though.
Oh, I also use it to solo Naval really easily too. Being able to use Lightning Draw Sword over and over really helps.
Its main use in endgame content was being able to swap to it while clearing trash mobs so it resets your skills before you reach the boss. But that’s hardly necessary anymore, since we never got the long ass maze dungeon maps for Luke Raid.
But yeah, it’s not a great set for dealing damage, so I wouldn’t bother with it unless it’s literally the last thing you’re missing after completing everything else (Full Plate, NG, Refined Ring, Silver Watch, Metal Line top/bottom, 12/12 setup) and you want to have some fun.