Pretty weak card, still useful for a very specific purpose. And it's actually pretty flexible for that purpose!
When you play a dedicated combat guardian, like a Mark Harrigan or William Yorick, you stick close to your clue specialists, you stick around picking up easy clues or beating down trouble that you or they find. This card helps you serve this role of tight-formation protector.
The trick to this card is that it works against voluntarily suffered attacks as well as enemy-round ones, this means, for example, that if you stick within one location of your buddy, if they draw an enemy, they can spend one action to move to your location, you intercept the attack of opportunity, and they carry on hoovering clues. If you're at the same location as an ally who's just drawn an enemy from the encounter deck that ally can just carry on as if nothing happened and keep digging for clues, you will intercept the attack anyway!
In other words, you need to not think of this card as a way for you to engage enemies and deal them damage, obviously this card does that job terribly! You need to think of this as a Fast auto-evade for your friends, who while you have this card in hand are able to do their jobs uninterrupted.
William Yorick likes this card because he has a test-less card package that can deal respectable damage without risking the luck of the bag. This involves the use of cards like Guard Dog, Lantern, Mano a Mano and/or Beat Cop.
Mark Harrigan specializes in killing threats and mitigating damage, it's easier to heal oneself than others and this card lets your friends drop off a target to spend all that Ammo on along with a bit of damage to heal.
I can't see other characters having the sheer staying power to support this card, Zoey Samaras can bear with it since she's one of the toughest characters in the game thanks to her resistance to horror via her great but she may find it hard to find space for this card in-between her tech cards.