I've done a few rides following just the line rather than with mapping. It's generally fine but every so often you come to a junction with roads close together (and sod's law both down steep hills so you don't want to double back) where it's tough to check the correct route.
Something cheap like a 2nd hand Dakota 10 would do the job or, as mentioned above, OSMAND is a good app if you're happy with checking your phone every so often.
I've done a few rides following just the line rather than with mapping. It's generally fine but every so often you come to a junction with roads close together (and sod's law both down steep hills so you don't want to double back) where it's tough to check the correct route.
Something cheap like a 2nd hand Dakota 10 would do the job or, as mentioned above, OSMAND is a good app if you're happy with checking your phone every so often.