How Viable Are Pure Coven / Cult Lists?

Hey , I have a 1250 point local tournament in a few months and have decided to start a Dark Eldar army for it as they look amazing and they are different to what I have played before. I'm really happy to see in the codex that there aren't any terrible options and most things do like viable but It has left me wondering which subsection of the army I would like to focus on. I'm trying to strike a balance between fun / fluffy and competitive which has interested in both cults and coven but I am worried that they might not be as efficient as Kabal due to lack of firepower.

I would really like to find out how you guys have got on with your armies and how good you would consider pure lists .

Thanks

Bard

At 1250pts Covens will break some armies into dust. They're so hard to crack it's crazy.