A nice signature asset, although it's a skill, since it belongs to Silas Marsh. It gives a decent boost to his worst stats and a icon for everything else, with the added bonus of an extra should you need it or a card if you don't. Being a skill, it has all the jankery we have come to expect from Silas, letting you fish on tests until you find the perfect moment to let it go off.
It's attached to a signature weakness that is fairly manageable, so it's up to personal preference whether you want to go with the "box," "book," or both signature sets.