The Kurviger app has a very low network usage. If you want to further reduce your mobile data usage, disable hillshading. Once the app has seen a part of the map, it is usually available offline, so when you are planning the route, you are already downloading parts of the map, that are reused during navigation.
If you happen to be offline or cannot go online, this might be possible. You should plan your route ahead, when you got access to internet. You can save a route as
.kurviger. Routes stored as
.kurviger can be used completely offline. For the navigation, you should have offline maps and offline routing data available for the region you are riding in. Otherwise you have to follow the route using the navigation instructions (they are available offline). You will see your location, the route itself, but no or only parts of the map. If you leave the route, the recalculation works if you are offline too, when going back to the route, the navigation should proceed seamlessly.