I really like this app. One small change I would add, for flexibility, is the ability to change your answers, or to delete an invitation (this could be reserved for the creator of the event). I also think that if you could send out reminders, and have an add to calendar option it would be stellar! Right now, unless you are in the app, you have no idea if someone had RSVP'd, or added a comment. Notifications would be helpful.
I'd rather use this instead of evite but the issue is everyone can't open or have the option to accept or decline. If this gets fixed, this will be my go to app for everything!