I couldn't remember if CH CD into D Dragon Tail was corner only or not. It's a bit riskier against characters with good reversals because they can just hit you out of the D Dragon Tail before it connects, since CD into D Dragon Tail is not a true blockstring. On a cornered opponent, D Dragon Tail is definitely safer on block, not sure how much advantage you actually get, though. Doesn't matter too much since CD by itself is pretty safe.