Their main appeal other than their look (if you like that sort of thing) is that they aren't necessarily villainous. In one of their stories they're a red herring, and I believe the ones the Doctor encounters in another episode are explicitly mentioned as being a renegade group. They're a caste-based warrior society that practices routine cybernetic enhancement, so there are a couple of aspects a writer could hook into to tell different types of stories if they wanted to.
I know the BBC likes to announce release dates close to the air date, but over a week *after* the air date?
I assume by "this month" you meant "January"?