There are costs and benefits when comparing this card to "Shrink". The benefit of "Shrink" is that it can be activated from the hand without being Set, as well as being unaffected by card effects that would destroy it (after activation), while this card can be used to potentially ward any further attacks during a given turn (and can be prolonged for future turns, if one chooses to pay its maintenance cost).
This card works well when your opponent attacks cards such as "Don Zaloog" and "Hydrogeddon". Your opponent's monsters will likely be destroyed, allowing your cards' effects to activate.
This can be made more potent when they are forced to attack a monster with an effect that gains advantage from inflicting battle damage or destroying monsters by battle, such as "Don Zaloog" and "Blackwing - Shura the Blue Flame".