You are right Folgelstrom, I don't use IAD j. D on reaction.
Sometimes, I see zato quickly crouch, so I do IAD j. D, because I expect the drill to come out.
I use it also when I just expect zato to drill.
Just in case, I checked in training mode, I was using IAD j. D to footloose to avoid landing on the drill. What I was afraid of doesn't even exist.
You were right all along Fogelstrom IAD j. S is just better, because even when j. S and the drill overlap nothing happen. May be when j. S hits Zato the drill hitbox is disabled before it disappears.