What do we know about them?
As far as I can tell, info seems to be scarce to non-existant, googling, even without quotes, just turns up sites with the words Dark and Mechanicus somewhere near each other, heh.
Are they a single entity or myriad different factions? Do they all worship Chaos, or do they just see it as a tool? Do some forsake Chaos altogether? Anything at all would be helpful, as I cant afford to buy Dark Adeptus until the end of the month.