This card potentially adds some insane combo potential, though the increased deck size makes your deck less consistent so it's also less likely to draw the card(s) you've chosen. It's better for investigators with lots of draw/ search effects, be it through their classes or their own ability. It's also better for assets, as you benefit from these longer than one time use of skills or events (though some investigator abilties may change that like Silas).
My favorite targets
Leo De Luca: Gain another action but his ressource cost is pretty steep.
Mr. "Rook": Search your deck for important cards and get your weaknesses out early, so they don't surprise you later. He's considered OP for a reason and is very likely to hit the taboo list. Be aware he's unique, so conflicts with other investigators.
Peter Sylvestre: To compensate low sanity of your investigator.
Dr. Milan Christopher: Useful for any high investigator. Mystics can use him too, though they don't benefit from +1 .
Scavenging: It's great for any clue-er but useless for the class it's in, as all survivors have medium to low int. Most clue-ers are almost guaranteed to trigger it every round. Use it to recur an item with many matching symbols or ?. Reload items with charges, secrets, etc. by discarding and replaying them, like Ancient stones or Grotesque Statue. This also works for mystics with Sixth Sense and similar spells.
Alice Luxley: Similar to scavenging, least usefull in the class she's in. Kill some Rats while investigating or help your fighter. Her high ressource cost could be a problem.
Magnifying Glass: Cheap boost while investigating
David Renfield: Gain lots of ressources if used right and +1 . I recommend Calling in Favors or Smoking Pipe get rid of his doom.
Lone Wolf: Another source of income if you're alone or small team. Mostly useless with Safeguard.
Fire Axe, Meat Cleaver, Baseball Bat: 2 damage weapons not on the taboo list, each with their own disadvantage.
Drawing Thin: Ressources or cards if you can afford to fail some tests or you don't care about the higher difficulty. Can add more secrets to Ancient Stone 1 if you beat the higher difficulty (use Hyperawareness or similar cards to beat the difficulty)
Teamwork: Opens some crazy combos by switching ressources, (XP) items and allies.
Hallowed Mirror: Everyone can heal HP/ Sanity now.
St. Hubert's Key: +1 and but pretty expensive.
Solemn Vow: Combo with Jessica Hyde and/ or Peter Sylvestre to heal other investigators.