On its own, this item is considerably worse at generating Cards, Runes, and Soul Hearts than Crystal Ball; Fortune Cookie produces 1 of either per 7.4 charges on average, while Crystal Ball produces 1 per 6 charges guaranteed. However, with 9 Volt, Fortune Cookie produces 1 per 3.7 charges on average, nearly twice as often as Crystal Ball.
Book of Virtues: Spawns a green wisp on the middle ring. Each wisp gives Isaac +0.2 Luck. If wisps are lost, Luck is only updated after Isaac's Luck changes through any means (this is most likely a bug; see bugs section of Book of Virtues). This mechanic also causes the first wisp given to not increase Luck.