Everytime people say "you should quit Facebook", I have two primary use cases:
1. Our high school class. Yes we used to use a mailing list but it's so much better with Facebook, with people freely sharing what interesting shit happens. We are a very closely knit class, at the 25th graduation anniversary like 25 of the 34 was there.
2. I have a group of friends doing all sorts of awesome shit (some of the more memorable include taking a medieval sword duel intro class, another shooting foam arrows at each other, there was laser tag, trampolines, Halloween mazes and much more) and the event functionality is just damn perfect: you create an event, everyone can post on it (I am coming, I am not coming, I need transport) all of the posts can be commented out. And people can just write posts into the group suggesting more events.
For both you'd need more than thirty people install a new app (remember how few apps are actually used) and actively use them at the same time or you will be missing events. This won't happen.