The Zerth blade is ok for low-mid level characters, especially with the Kensai/Mage dual class. If you have the items upgrade/tactics mod, it becomes largely redundant... mainly because of Celestial Fury +5 and Sanchuudoku +4.
The item upgrade also introduces the 'improved robe of evil/neutral/good archmagi' which provides you with an extra 1st, 2nd, 3rd and 4th level spell. This cancels out the penalty of not using the Zerth blade entirely.
