That's what you get when you mix powers intended for NPCs in with the rest of the powers.
You mistake my meaning.
I mean, it's not fun to play as the GM, with it on an NPC. That's how I used it, and it was quite annoying.
In a game, "not fun" is the biggest problem around.
Anyway, the poor representation problem is from the fact that Demonic Co-Pilot isn't really a threat to a disciplined character unless they use it for things they're good at. Your average Wizard could make Fists attacks all day with it, but a trained martial artist would have enormous trouble doing the same thing. Even if he had excellent Discipline.
That seems like a poor simulation to me.
Plus, using a hexenwulf belt to transform actually does not trigger Demonic Co-Pilot at all. The FBI guys have nothing to fear unless they start sprinting or fighting or something.
And Demonic Co-Pilot does not simulate things like the FBI peoples' psychotic aggression in human form or their addiction to transformation. At least, it doesn't simulate them well. You could hack things with take-out narration and consequence Compels, but neither method is as effective as Sponsor Debt.