That being said, I was more interested in mechanical aspects. How are the Dark Eldar classes from a mechanical point of view? Are they too strong/weak? Any interesting things they can pull off/the GM should be aware of?
I don't 'believe' in playing mathhammer (nor am I accusing you), but they're very good at combat and things requiring Agility, so sneaking and piloting.
So from a gaming perspective they have a handful of good niches that they can fulfill easily, based on raw stats. Career and Advanced Ranks are mostly combat focused obviously. But you have enough flexibility that you're not pidgeon-holed in to playing Killy McStabstab the whole game.
An idea of mine I've never got to play is basically a reaver, leaning toward fighter piloting later. Something I think he'd be pretty good at, considering the previously alluded bonuses to Agility that Eldar have.
Case in point: when I was considering this dark Eldar we already had a character that did the piloting for the party(and little else). Bringing in a character that did piloting better in adition to other stuff wouldn't have.been the micest move