How was charlatan's die intended to be used?

As a magic item the character uses to cheat at gambling 

or

As a way for players to determine the outcome of a d6 roll?

It's a magic item used in-game (largely, as you point out, to cheat at gambling).

Common-tier magic items don't generally have the power to break the fourth wall and affect things in the real world.

The description clearly states that you control which number the Charlatan's Die lands on, and I'm pretty sure you don't have one in the real world, so it's purely for in-game-world use.

im gonna get a full set and then make my dnd character play dnd in dnd and crit constantly