I was looking at Cartomancer as a handy way to use normally tactically unwieldy spells in the heat of a fight. Here's the relevant quotes:
- Card Tricks. You learn the Prestidigitation cantrip and can use it to create illusions that duplicate the effects of stage magic. When you use Prestidigitation in this way, you can conceal the verbal and somatic components of the spell as ordinary conversation and card handling.
- Hidden Ace. When you finish a long rest, you can choose one spell from your class’s spell list and imbue that spell into a card. The chosen spell must have a casting time of 1 action, and it must be a level for which you have spell slots. The card remains imbued with this spell for 8 hours. While the card is imbued with the spell, you can use a bonus action to flourish the card and cast the spell within. The card then immediately loses its magic.
However, upon closer inspection, it seems like a worse version of Metamagic Adept, which can provide one casting of Quickened Spell at any time, as well as being more flexible with another Metamagic Option:
You learn two Metamagic options of your choice from the sorcerer class. You can use only one Metamagic option on a spell when you cast it, unless the option says otherwise. Whenever you reach a level that grants the Ability Score Improvement feature, you can replace one of these Metamagic options with another one from the sorcerer class. You gain 2 sorcery points to spend on Metamagic (these points are added to any sorcery points you have from another source but can be used only on Metamagic). You regain all spent sorcery points when you finish a long rest.
Lastly, as the final doubting point, the Cartomancy feat seems to exclude anyone else from using your cards, so the option of handing someone an emergency Healing Hand or other is kaput. What's the benefit of choosing Cartomancy over Metamagic Adept? There's probably a niche option for maximizing the efficacy of prestidigitation, but I'm speaking more about the primary feature of Cartomancy.