Definitely has its merits IF you can pair it correctly.
I mean, maybe you could play this on its own as some sort of one-round Hail Mary where you don't have to fear all the curse tokens you ended up sinking into the bag, like some kind of weird, reversed Will to Survive, but then you have to deal with the fact that ALL of your blessed tokens are corrupted back to curse tokens, and NOT just the ones you initially converted.
However, even with just the base box, it really doesn't seem hard to fill the bag with curse tokens (Faustian Bargain, Deep Knowledge, Promise of Power, etc.), so I do think this can work really well as a combo card with cards that would spend bless tokens from the bag, maybe curse tokens if you're willing to wipe the bag of bless tokens. As of this review, only the base Innsmouth box has been released, so the only good combos I can think of is 1.) playing this immediately before playing Rite of Sanctification, especially if you pulled a nastily timed Crisis of Faith as Sister Mary, and 2.) use the Cryptic Grimoire's second action after the round ends if the curse+bless tokens in the bag = 10+ beforehand.
But honestly, I wouldn't be surprised if there are more cards that require large costs of bless (or curse) tokens down the line, so I'm anticipating seeing even more use for this in the completed campaign. If you think of any more combos (now or in the future), share them in the comments!