Oooh. Are we about to get some vigilante hypnotism? Making her ex confess to his misdeeds probably won't help her forget him, but making her parents lose trust in him is probably good.
If I were him, I'd probably use the app to make her lose all affection for him, then make him fall back in love with her.
Geez, people really didn't understand the synopsis, did they? The actual point is to not go the stereotypical hypnosis hentai way. Why the heck would they have our MC, who's meant to be a good guy, take advantage of a girl like that?
I'm pretty sure the mass 1-star ratings weren't there before. That's just sad, man.