Agreed. An NPC like this is the "In case of emergency, break glass" type. It should only be used if the players are seriously abusing the game.
GM: "You're trailing your mark through the streets of Detroit. Up ahead, you see a large crowd gathering for a PR speech on the steps of Ares' Headquarters. He's heading towards the crowd to try and lose you."
Player 1: "I continue to follow him, trying to close the distance so I don't lose him."
Player 2: "I'm still watching, keeping P1 covered from my sniper's roost. Just had a thought, what's the speech about?"
GM: "Huh? Um... Some new announcement being made about a military contract." <rolls dice> "Your mark's entered the crowd, but you still see him."
Player 1: "Cool. I continue to watch, but I'm ready to move if he tries to break for it."
Player 2: "Is Damien Knight giving the speech?"
GM: <barely glances at player 2> "Sure he is." <rolls dice> "Uh-oh, the mark spots you. He starts pushing -"
Player 2: "I shoot him."
GM: "The mark?"
Player 2: "No, Damien Knight. My character's got an obsession about Ares and hates Knight. I try to take him out. And I'm using Edge"
GM: "WHAT?!?"
Player 2: <rolls obscene dice for being specialized sniper> "Sweet! Rule of Six baby! Suck 15 successes Damien!"
GM: "!!!"
Player 1: "
"
Player 2: "So, did I kill him?"
GM: "No. It turns out that it was an illusion. Damien's been getting threats recently and decided to hold this stunt to trap any would-be assassins. The magical illusion drops and you see through your sites something that was once human. And it looks directly at you. Then begins to come after you."
Player 2: "DAMMIT!"