The Main difference is Depth of Engraving :
Wax Stamps are typically engraved at 0.75mm to 1mm in depth.
Chocolate Stamps are engraved  10-20% deeper. Chocolate does not hold an impression as well as Sealing Wax.
Food-Safe Coating:  In addition, a food safe coating is applied to the Brass for Chocolate Stamps
You can use Chocolate stamps on wax as well, but in doing so you will negate the effect of the food-safe coating that is applied.
The artwork should be submitted with the background in white and the art to be engraved in black .