Where?
Rounds app

Why
Success message upon completion of the security check is very short, but also surprising, funny, conveys a true sense of cooperation. Also, it tells the users how they benefited: by having a secured account.

Why?
After giving feedback on one of the product new features, they say what it actually means: You just improved the feature.

Why?
The message is funny, but also says that they kept their promise for a simple, intuitive platform and that getting their product was an excellent choice that made your life much easier.