Aruzasu's Shield is not really worth its price—it is of questionable value since you won't see many Bees going forward, and Water Spirits rarely fire projectiles at all. Buying it does change the overworld music, though, which is a nice touch.
Unlike Aruzasu's Shield, Remedia's Shield blocks projectiles you will see a lot of. In fact, it blocks every projectile fired by any overworld Enemy. It's still a bit overpriced, but worth it in the long run.