Unlike within studio, you are actually charged and robux is taken out of your account when you buy a product (devproduct or gamepass) you made in your own game. This is not optimal as you shouldn’t have to pay for something you made yourself (multiple times on some occasions).
If all products created by the developer are free for the developer when purchased in-game, it would drastically help with in-game testing as there are some scenarios that are not easily testable in studio and require the purchase of a developer product or gamepass.