The first quarter of the game you can't use them and when you finally see them in action they are smurfing. trout. up. Odin destroyed Cleyra with just his spear! Atomos sucks Lindblum dry!
THESE GUYS ARE GONNA BE SO smurfING SWEET
Nope. Odin does like, 300 damage. THE smurf.
I've always been horribly disappointed with the eidolons. Although the moment Beatrix gives you back all of your gemstones it's like, "WHY CAN'T I HOLD ALL OF THESE EIDOLONS."
EDIT: Can a mod correct the title, please?