@Con-Hennekens Thanks Con. In the end I used the trip's recommended app (Guibo), mainly because it was pre-supplied with maps, it used tracks and OSM, and so there was little to be gained by using MRA. Guibo doesn't cope well if you accidentally leave the track either - it's up to you to correct your navigation.
And guess what - Guibo ran the battery dry after half a day just using a track. It's not just MRA that has battery problems! Luckily, I had anticipated this and took a power bank on holiday, as you do.
Lastly, I can recommend the north Adriatica coast (Venice -> Istria / Poreč) as a lovely area to cycle. Ice cream, seafood, quiet roads and cycle tracks everywhere.