Hey, so this is super matchup dependent and is a little difficult to answer, but I'll use two examples to try and help (1 example of shotgun DDV, and one example of hold DDV). Vayu Turbo is an example of a matchup where I would shotgun DDV. The reason is because there's too much that can go wrong if you do not shotgun DDV (Trooper prio, Grepher prio, Armageddon Knight summon, etc.) You might be able to kill their normal summon because if they open Ryko or Hamster, setting either of those two is pretty solid, but the risk of any of those other options is too severe. You also don't get information of their backrow if you wait to use the DDV against Vayu. So that's an example of a matchup where I think shotgun DDV is good. A matchup where I think you hold it is Blackwing. Pure Blackwing targets are Blizzard, Gale, Kalut and Vayu. None of these cards will do something relevant on turn 1, and none of them do anything relevant on summon except for Blizzard (Gale arguably, but it will target armed wing most likely). This is also a matchup where having the pressure of 2300 armed wing is good because it outclasses every Blackwing monster except Blizzard -> Synchro, Sirocco -> Pump or Gale -> Halve. In all of these situations you can wait to DDV until the summon. In addition, waiting for the summon if they're committing their big monsters with whirlwind means they start searching for DDV targets vs shotgun DDV where they can still search for the targets under whirlwind. The punish to waiting for DDV is chain icarus attack, but generally you should be playing in a way where you don't really care if you get icarused in that position. It should only hit grepher. That might not help because it's hard to explain since it depends on the matchup, but generally decks that get value from committing the DDV targets like Vayu or Frog, you can shotgun DDV. Other times you can hold. Against a deck where I have no info, I would just shotgun it. Full info is usually worth it.

Awesome analysis, thanks!