Guru Maps is a third party mapping application that can use any map source (with the proper integration file).

https://gurumaps.app/

Creating a Guru Maps .ms (map source) file would allow NZ Topo Maps to be loaded into Guru Maps. This would add the following functionality instantly:
- offline map use (downloadable map)
- live geo-tracking offline
- gpx file generation (log/save/export)
- importing of gpx/kml/kmz layers over NZ Topo Map
- as-the-crow-flies distance measurement between any two points
- saving of pins (in collections)
- alternating between NZ Topo and other map sources with the same data layers still intact

Basically adding NZ Topo as a source for Guru adds many of the requested functionalities here in one go. Def worth it!