I have been using notifications/push alerts quite extensively, and I have found that when delays occur they aren’t always reported to the endpoint. For example:
flightaware.com/live/flight/id/S … rline-0124
I received the “filed” alert, but the flight was then delayed shortly after (which is reflected on the FlightAware page) and I didn’t receive any “delayed” or “change” alerts.
Also, without any ability to subscribe to the alerts for the inbound aircraft (see my other thread post) there is no way to have a backup.