All demigods its a good investment if you can spare the slot..It doesn't make sense for some DGs to get it. Not much point as UB, for example, compared to what 18k could get you instead. It's not really worth it for Regulus either.
Depends on how you've itemized both...and for reggie? Build him with poisoned dagger, and early you have hats for mana, later this +mage +ash, never at a loss for mana...
Every hit gives him enough to keep the wings up and in crowds spam mines as soon as its up..