
You're paying 2 resources to automatically succeed a test in the future. It cost 1 action to play & you'll get that action back as part of Mateo's ability.
You don't wanna hold on to it for long, maybe a turn or two, as removing the hurts your team. This is exponential with more players. It's also better played at towards the end of the scenario when skill tests become harder & more important.
Mateo does have access to Shrine of the Moirai to return the codex to his hand potentially getting the 4x in a scenario!