I'll mention I bought a Milwaukee 2967-20 1/2" impact specifically to change out the factory installed anode on our heater. Our anode broke free with no issues.The Milwaukee impact has an unusual feature that once the bolt ( or anode ) is loose it immediately slows to a moderate speed ( much less vibration).
I do not regret the expense at all because the impact is superior to my several electric & air impacts. Perfect for rotating tires.
More info = We service our electric heater every six months ( replacing the elements and vacuuming out the sediment ) & our prior anode lasted three years.