I imagine the intent of something like this is not really that people should install it, just a fully working PoC to show that your deleted messages are not really deleted and you should act appropriately if you type something you shouldn't have. It's just smart practice anyway, as even if the delete was foolproof you don't know who managed to see the message before you deleted it.

(I will admit to an illicit thrill when I click no on the outlook pop-up that informs me someone wants to recall their message...)