Is my action of “bailing” transparent to the other party? Via (re)prompting my friend with a notification or something where they might be able to guess I was trying to get out?
I don't know... I'd be offended that my friend couldn't just tell me directly. But I guess if I'm using the app as well... but doesn't that call into question the nature of the relationship?
This could leak information to the other party if bailing is still available during the event. By trying to bail myself after you show up I could "prove" you really didn't want to be here after all.
Similar to the problem with the 'secret crush' version of the same idea -- people can insincerely tick every box, simply to see which of their friends has a crush on them. I guess the same caveat applies: only use this app with people you trust. (Of course, some would say that if you really trust each other you don't need this app; but I don't know, I can see a use case for those situations where your plans have become inconvenient, but not sufficiently inconvenient to back out at short notice without seeming rude. I wouldn't use it myself but I don't even use a calendar app.)
But if you both decide you no longer want to meet up, you no longer have to, and nobody gets offended