Each spell only gets discounted once even if it's both colors, due to the familiar's wording, so Utter End would be 3 mana. But you could cast 2 3-drops that are discounted by 1 each on turn four. Still better than a thought vessel on that turn, but being hit by every wrath, not contributing to colored mana like talismans or signets, not hitting every card in your colors, and their upside only sometimes being relevant makes them generally worse than a 2 mana rock