I am no fan of the messaging component of the app. In concept, it is exactly what I want - a way to text other members of my party without also receiving texts from the rest of the world (i.e., shoreside).
However, the app has some serious limitation in terms of delivering messages in a timely manner and/or notifying you that a message has been delivered. In our experience on several cruises, it seems that the app must always be “surfaced” on your phone to work as advertised, meaning it must always be the current app displayed on your phone’s screen.
If the app is not surfaced (e.g., you opened a game of solitaire or whatever), you don’t get notifications that a message has been received. And in fact, we frequently ran into issues where we opened/surfaced the app, and messages that had been sent to us hours ago still had not been delivered.
If your messaging app cannot deliver messages promptly and reliably, you’ve failed, period.
I think the fact that they are rolling out free iMessage is quite telling.