I finally remembered to take a screenshot with my Shield of Impenetrable Darkness, comparing it my old Crest of the Sha'tar.
I gain pure avoidance, armor, uncrushable avoidance, and block value for a bit of health. The increase in the armor and block value should more than make up for the health lost.
Not to be overlooked, the shield looks beautiful. I've seen some around Shat, but I don't recall seeing one on a Paladin yet.
Raid buffed, I have 20,377 hit points, 5508 mana, and 17687 Armor, along with 388 Spell Damage, 511 Defense, 22% Dodge, 16% Parry, and 22% Block.