The AI has this thing where it prioritizes a target that is concentrating on a spell over just about anything. So being in melee range + concentration + need to perform touch attacks is a recipe for disaster with that spell. For it to be effective at all you would need Mirror Image Up and high AC anyway - and even then the damage is nothing special. 3d6 Necrotic with no modifier damage you will average 12 damage and heal 6- that's just not worth it. You are better off with the Githyanki + Potion of Hill Giant Strength + Sword of Justice to do 2d6 + 6 = 8-18 damage and concentrate on Tyr's protection for +2 AC - while tossing fireballs for 8d6 damage.
