It's an excellent multiplayer mechanic because it allows for creature decks to avoid kingmaking scenarios, or purposefully engage with them in order to play politics or create periods for player interaction
Getting to four or five power on a single creature is difficult, and its even more difficult to churn out multiple times to keep Crewing your Vehicle
therefore, vampires have always existed in Magic
MOM has a bonus sheet, Multiversal Legends (MUL), consisting of reprints of legendary creatures, some of which (like Atraxa, Praetors' Voice or Ragavan, Nimble Pilferer) are long-time MTG staples
If you only take one thing from this: Sleeve durability is usually medium until you seal it correctly
As for the downsides, it only untaps one of your creatures and is a sorcery