I would agree that Ballymun would not be my choice but it is changing, by how much who knows. Over the years this area was always on the verge of being turned around, but unfortunately it never really did. There are certain parts that are no go, but those are few. On the plus side, it is a short distance to the City, DCU, M50, Blanch SC, Airport and mixed areas like Phibsboro, Glasnevin, Finglas.
As far as I know there is Section 23 relief also on new developments, which are on the main street, like anywhere else is it going to change? Who knows? But I personally would not take the risk.