The mobile app worked quite well for me when it comes to notifications and event planning. It has come a long, long way from its buggy beginnings! That said, it can of course always become better:
1) I learned on the last day that the app has a Contact Security feature. It can be reached (in the iOS version) by the not exactly simple or intuitive way of tapping More -> Information -> Security -> Contacting Security -> Call Security (Phone). Notably, "Contacting Security" is literally the only sub-point in the Security menu that contains another function besides text. I assume that most people, when they have reason to contact security, would want a way that is as short and intuitive as possible - putting it as the third item right in the More menu seems reasonable and wouldn't clutter up the menu.
2) Less of a useability problem, more of a feature request: The "Dealers" submenu seems a little specific for something that can be reached via one tap. Perhaps it could be expanded to list other service providers at the convention as well, like artists taking commissions outside the den (and their contact info via telegram, email or the like) or artists hanging their stuff in the art show. Ideally, this could be combined with a search function that allows to filter people using checkboxes like "is a dealer in the den", "takes commissions", "does art trades", "is a digital artist", "is a traditional artist" and so on. And the summa cum laude version (likely rather more difficult to implement, though the app already has a login function) would allow people to update their own info in real time, possibly to indicate they have no more slots for commissions available at the moment or that they can currently be found in the artist lounge or the alley and the like.
Once again, thanks for the app! It's made my convention life a lot more relaxed.