The Key of Solomon is one of the best cards for the Blurse archetype, to the point where characters who normally wouldn't care about Blessings or Curses should potentially think about running Blurse solely to fuel it.

For Curse investigators, The Key of Solomon is the best economy card in the game that refunds itself on the same turn it's played, with the added bonus of removing 1 Curse token from the bag per turn at Fast speed. As soon the Key of Solomon is in play (preferably with a card like Spirit of Humanity to consistently fuel it), Curse investigators can give Rogues like Jenny Barnes or Preston Fairmont a serious run for their money in the resource generation department.

For Blessing investigators, The Key of Solomon is the best healing card in the game on par with Hallowed Mirror paired with Soothing Melody. Being able to consistently heal investigators and allies for any combination of 2 damage and/or 2 horror every turn without needing to spend actions is pretty incredible. Unfortunately, it's a bit harder to keep the chaos bag flooded with Blessings than Curses, but the payoff is strong enough for Blessing tech that even investigators like Carolyn Fern and Vincent Lee should seriously consider running at least running Spirit of Humanity, Radiant Smite, and The Key of Solomon for the synergy alone.

And if your table happens to be running any combination of Blessing and Curses, you get the best of both worlds. I'd be shocked if The Key of Solomon wasn't on the next Taboo list, so abuse it while you still can.