Ian,
We are beta on both iOS and Android for the 19.1 release please check out the information here if you want to join the beta: Navigator for ArcGIS Beta . This release represents a major evolution of the app and some of the highlights are listed here: https://community.esri.com/groups/navigator-for-arcgis-beta/blog/2018/10/03/whats-new-and-whats-comi...
Hope this helps,
-Brent
