Sana... that's just half of the answer.
You don't need those 100% Eidos to use a character ATK/HP Eido.
If you run ele adv and you don't have enough HP then use those. They are pretty nice too push your HP and you won't lose a lot of damage because of ele adv.
If you have a 100% eido, then use whatever you want.
Without ele adv then you can also use those character ATK/HP Eido. Otherwise I would just go with 2x 100% if possible.