We had an existing App, written in (Apple) Swift, that was running fine, and calling an API. We'd done that as the first App, since our website users were clearly heavily dominated by iOS users.
Our use case is student safety, though increasingly we're seeing our platform used by companies for employee safety!
However, the trigger for moving away from Swift was two fold: * we wanted to introduce a real time messaging solution (for fire alerts) * we wanted to launch an Android app
Expo.io gave us the tools to build a single App that could run on both Android and iOS. Our App update on the Apple Store was accepted as a replacement for the Swift one, and the Google Play store was likewise straightforward (due, in no small part, to the clear documentation on the Expo site.)
Our use case comes from schools - so we use the term "pupils" and "staff" in a way that an organisation might use "people" and "managers." Expo appears to give us a clear way forward to an instant notification world in which "staff" (who mainly use our website) will be able to send instant notifications to "pupils" (who mainly use our app.)