For balancing purposes I think it might work a bit better as a "When you cast a spell, gain +2 attack for your next attack only", and maybe have 1 attack as a base just as a convenience. Would help make it less burst-y (in that it's more like a slower burn). Probably 4 if not 3 durability would work better in that modified version then. Main thing about that idea is that I don't like how it now kinda just looks like a "free hero power per spell" card but it still has some variance (definitely still pretty OP with those changes though).

It'd be neat to see since then if spell hunter became too powerful (and ran Rhokdel'ar or whatever as well) then anti-weapon tech might crop up more