I cannot understand why this lasts 4 turns when Wings lasts 5.
Wings blocks 52 creatures and 13 weapons.
Arched Wall blocks 31 creatures and 2 weapons.
Also, Wings can count on Spiders and Recluses that blocks even more creatures (removing Airborne), this shield cannot benefit of a similar sinergy.
So this shield should lasts the same number of turns and cost less than Wings OR lasts more turns than Wings while costing the same quanta.