Shame hunter has no weapon buffs. However, it's pretty neat with hunter's mark. 2 card combo for a free removal against anything not behind taunt. Makes spell Hunter better and might be run in a slower midrange/control hunter (if that's a thing)
Anyway I don't think this is that good... Light's Justice is not good and health doesn't matter too much in hunter, unless that all spells deck is viable, but I don't think it will, for now at least.
HP matters in Hunter's due to all the aggro/tempo/zoo decks. One of the reasons why the class is lacking is the inability to deal 1 damage and clear the minion. This weapon will overcome both HP loss and lack of 1 HP minion clears.
It's a pretty good weapon. Might be the best weapon in the game. Immunity is underrated, it is a very strong mechanic that's why you don't see it a lot.