I've seen some complaints about it in the press (on the lines of it taking over the role that BBC2 should have), but it has such a strong brand that I suspect you're right, and it's safe. I'd like to see dramas like this be successful, if it means that BBC4 will start to commission more of this kind of thing.

I can't see what BBC3 offers, to be honest - but then I'm not its demographic, I guess *g*