Q: What is the timing interaction for Expert Defense?

A: You must exhaust your hero to defend in order to play Expert Defense to boost your DEF by 3 for that attack. Also, you must play it immediately after declaring your hero as a defender, which occurs before boost cards are revealed. -(Developer Ruling, Hall of Heroes)

This is maybe the first Protection card that boosted defending. 3 defense for 1ER is excellent value. I got it, that it doesn't had additional bonus like Side Step, Jump Flip and many other cards,but it provides a force without sacrifice flexibility in the hand.

Also this kind of effency is valuable for heroes with defending worse thant 3 which leads to second point: Expert Defense is worth throwing to the deck even outside of archetype.

Rating (A-C) A- Still worth using after many years and has no really downside. If I made the Protection from the scratch, this will be one of the first card that I think about creating (next to the Armored Vest of course).