Piety based dark knight

[Kitfox]

I can say it does work for me and allows me to get out more dps are a tank.

Do you have data to back this up?

Don't make claims like this if it's only based on subjective feeling. You need to compare the actual increase in mana regen to the DPS gains from lost secondary stats. Before you do, your words mean nothing.

It increases max mp, because of dark side you have 0 natural regen.

This is incorrect. You do have natural mana regen with Darkside up. However, outside sources have no effect on you, such as Ballad or Mana Turret. You can test this by putting up Darkside and comparing how your mana behaves in and out of battle. In battle your natural regen is lower and you will lose MP, however, outside battle you will actually gain MP as the regen is stronger.