I think this is being misinterpreted a little bit. This only blocks attacks that exactly equal the final number. So for their example, AC 14, and final total being 23, 15-22 still hits and 24+ still hits.
It’s an interesting magic item but ultimately it’s too much additional math and dice for a turn.
That is not the recipe I know lol. It seems way harder to get any quantity of animal blood than Styrofoam.