Rob, I use a dedicated gps unit as my primary navigational tool and a phone with VR as my back up (with my intended route always loaded on both). I also carry printed A4 sheets of the relevant map in plastic wallets, with my route printed on them, usuallly at 1:12500. Despite this, I always have a compass and the relevant OS sheet in my pack. The latter two items have not been used in anger ever since I got a gps with a map display but they are my final recourse.
The OS sheet can be used for a radical replanning of my route if I ever need to and the compass can not only be used to navigate if necessary but also to take bearings on distant feature to identify them. Once you divert from your intended route a gps or phone is just a moving map display so you will need to map-read to interpret it. As to the compass, using one isn't rocket science.
Finally remember, ViewRanger is just software - it doesn't know up from down let alone East from West. I relies on your phone gps and compass (if it has one)or location information.