I'm a little surprised that discussion of this card so far has been focused on two issues that seem to me secondary.
1) How bless and curse tokens change your odds of passing checks.
2) The advantages of deck-thinning.
The main reason to play this card, in my view, is because you're going for a build that exploits either bless or curse tokens to achieve other, card-based effects. And if you are, it's wonderful! Here are some nice combos that you can pull off with current and upcoming cards:
1) Rite of Sanctification: If you happen to have both the Rite and Tempt Fate in your opening hand, you can immediately seal three Bless tokens on the Rite for a total savings of six resources over time. Not bad! If the combo emerges later in the game, it's less valuable, but still likely to be helpful.
2) Radiant Smite: If you have Tempt and Smite in your hand at the same time, you can drop the Tempt to make an absolutely bonkers attack with +3 Will and 4 damage.
3) Ward of Radiance: Unfortunately, I don't think you can use the player window in the Mythos phase to draw your card, dump bless tokens in the bag with Tempt, and then cancel with the Ward. BUT if you have the Ward and Tempt in hand heading into a Mythos phase and think you might want to cancel what you draw, you can increase your odds of doing so by plumping the bag.
4) Beloved: If you desperately need to pass a check but lack the skill value, you can increase your odds of an auto-success by dumping some bless tokens in the bag before you draw (heck, even if you draw a curse token, your second pull could be a bless).
5) Ancient Covenant: Once a turn, bless tokens are pretty much auto-successes. They therefore become MUCH more valuable, and worth the 3 curse tokens.
Curse Deck: As a general rule, curse decks love this card even more than bless decks do. Bless decks are willing to deal with the three curse tokens in order to achieve some other benefit, but if cursing is your jam, it's not like you HATE having bless tokens in the bag as well. Tempt Fate simply becomes a win-win!
1) Blasphemous Covenant: Tempt Fate works great with this card. Just play Tempt Fate as soon as you draw it, and feel the math of the bag bend in your advantage...
2) Skeptic: This seems like a weak card to me, especially at 1xp, but if you happen to be running it, Tempt Fate does make it mathematically more advantageous.
3) Eye of Chaos: Once again, the bless tokens help you pass checks; the curse tokens get you clues. If you're into ocular entropy, you're happy about all SIX of the tokens that Tempt puts in your bag.
4) Gaze of Ouraxsh: I have no idea whether this card is good or not, but I do know that the cursier the bag, the better it gets!
5) Cryptic Grimoire: Man, this thing seems hard to translate, even with a couple tempts in your deck. But the tempts will certainly help.
Summary: To me, it's kind of an academic question whether this card is good or bad in a deck that has nothing else to do with blessing and cursing. Clearly, it's a FANTASTIC card, probably even an auto-include, in decks that are using bless and curse tokens to do other things.