### I would never choose this spell because NPCs generally don't make Charisma checks.

I've been DM for a lot of games, and played in a lot more, and the thing this spell tries to do just doesn't happen. *NPCs are generally trying to persuade/deceive/intimidate against the player's agency, not making charisma checks themselves*. Think about some of the examples you mention in the question. Self-righteous town guard makes an announcement: does he make a charisma check or do the players roll Insight? Merchant is haggling over the value of an item: does the merchant roll deception for its value, or does the player roll Insight or Persuasion or Deception or Intimidation? In these scenarios, *it is the players that do the rolling*, because it is the players that are here to play the game. Having the NPC rolling for the Persuasion check can take away form the player's agency:

>Player: I think the shopkeep is lying about where he got this sword.
>
>DM: Well, he rolled a natural 20 in deception, so yes you do.

Having the NPCs making the Charisma checks just doesn't work well with player agency. So to answer your question, "is this a well designed spell?", no it is not. It fails to consider how the game is actually played. It might work as a minor set piece that an NPC might use against the player characters, but NPCs do not themselves make enough charisma checks for this to *ever* be a viable choice of spell for a player character.