The part about sacrificing a shield to negate the extra effect surprised me, just because I had interpreted it already as the effect goes through without the extra damage. I only read it that way because the Furious Critical feature says when you score a critical hit, and sacrificing a shield says when you take a critical hit you can use your reaction to turn the critical hit into a normal hit. I read that as the critical hit is already "scored" and even taken by the defender, so Furious Critical takes effect, then the reaction is used to turn the normal critical bonus into a normal hit.