I think the blocking-punisher effect is much worse than
Falter. With Falter you can ignore combat math and alpha strike, but here they can maximize their blocking choices to kill your creatures and take into account the card advantage, and at a potentially severe loss of tempo for you. Also, if you're playing Falter then usually your strategy is to reach, which means you need every last bit of damage, but with Benefactor's Draught they would still chump your most damaging threat at the cost of one card. It's also unlikely that vigilance would be as important if your strategy wants Falter.
Being a cantrip is great though. I would probably be more likely to draft it for a midrange deck.
It would be a
lot better if your cube has a lot of combat tricks.