Sad to see companies like this go. The founder stated in the article above that the cost of the data being expensive was part of the demise, I wonder if croud-sourced solutions such as https://flightaware.com/commercial/flightxml/ (FlightAware) was ever used. That said any time I walk into an FBO or look on the screens for arriving or departing flights in general aviation, FlightAware data is the only thing I see people use. It could be because FlightAware owns the data (which is crowdsourced in a similar fashion to WeatherUnderground stations) they provide a service that Just Landed simply can't compete with.
As with anything in Travel outside of actual aviation aspects these types of services such as just landed, to me, feel more like Value Ads than core products. I personally just use google to track the flight of an arrival and can do it from my phone's browser by typing the flight number in a google search box.
Since a screenshot of the Just Landed app shows up in the image carousel on your link, I am assuming that they used FlightAware for their data. FlightAware charges people for API access, and also specifically provides a set of tools for FBOs (https://flightaware.com/commercial/fbotoolbox).
As with anything in Travel outside of actual aviation aspects these types of services such as just landed, to me, feel more like Value Ads than core products. I personally just use google to track the flight of an arrival and can do it from my phone's browser by typing the flight number in a google search box.