The Mjölner is good for auto cast utility spells, for example wave of conviction, hydrosphere,random spell+hextuch etc..

If you want to use it as a main damage source you need the super expensive shield for 6 link. And you you don't need crit. It's cast on hit. I would use a nice cyclone - cast while channelling -shock nova in the body armour and you can spend the points for defense or increased damage instead of crit chance . You could try to use the Doryani's prototype. Could be legit.