These are the cards that shut down aggro decks and hastey creatures
And if you just want to play normal match types like Standard or Alchemy and build a deck with the odd booster you earn along the way, you never have to get out your wallet or feel like you should, anyway
Its also not likely for anyone other than a dedicated token deck to have creatures left after this resolves
And while it may run counter to a Dog decks core theme, you can also create some stray Cat tokens later on as well, if you need hasty bodies to close out a game
Its the same as the rules for turning a Morph or Disguise creature face-up: any effects which trigger from unlocking the door WILL use the stack and allow opponents to respond as normal, so this ends up sounding scarier than it is in practice
What separates these two cards is their mana costs Ornithopter costs two generic mana to cast, while Birds of Paradise only costs one