I recommend to buy this DLC because:
- It will be easier to get the Stella's Dungeon achievement, which is really hard to obtain otherwise, since she keeps dying for unknown reasons; practically it halves the times it takes for Stella to finish the dungeon, but more importantly it lets you keep your items after death, both the ones you already had and the ones you collected, so it's really good stuff.

-Your Exp will be multiplied by six; I recommend to use that plan only after finishing the entire story, because basically it lets you avoid all the grinding before the boss battle, which is the most fun thing in the game. I am actually using it, for example, to grind from 100 to 999