Actually, IF you played it a certain way, I think it could work. I mean, think about it. The kind of tattooing you'd need to do would be extensive and complicated. If it was broken even a little, even by a papercut, the design would be interrupted. At best you'd get a malfunctioning focus and at worst, you'd lose the focus benefit until you could "repair" it, which in this case means heal the damage. The player might think that overly harsh, but I think it's in keeping with the themes of the Dresdenverse in the game. So you'd either get a guy that brewed more healing potions than Pepsi brews soda, or a guy who was constantly losing his focus benefits every time he took a hit to the tattoos.
If the player didn't want to play it like that, I'd side with the consensus on not working very well.