If this card had 3 icons and said "Commit only to a skill test you are performing during the Mythos phase," I would still consider taking this card in some Guardian decks.
This card can do that and it can played to boost some early action checks. I think it's quite good. Guardian characters normally want to go first anyways in order to clear out enemies, so they get good use out of it.
It's true that this card loses a little bit of utility if there are multiple people using it, but I think that it doesn't diminish it enough to say that only one investigator can use it exclusively.
I find this card is easier to consistently use more than Inquiring Mind, Last Chance, and Rise to the Occasion. One thing you can normally count on in Arkham Horror: There will be encounter cards, and they will try to kill you.