It's pretty ok, DB is a very strong fast move. It's a dragon itself, so it doesn't counter dragons, it'll lose a DB spamming match against better dragons like Altaria and Kingdra. I find its main draw to be that it gets Flamethrower as a secondary charge move, which can take out steel types that would wall Altaria and Kingdra.
EDIT: If you want to take down Altaria, there are a fair number of options. Azumarill, Skarmory, Steelix, A-Sandslash, A-Ninetales, any unshielded ice charge move (from Medicham, Hitmonchan, Blastoise, Whiscash, Cresselia, Tentacruel for example).
