IME & reading turn-by-turn navigation (esp pre-programmed routes) often doesn't work well. Handlebar cue-sheet holder + reg bike computer is pretty simple & convenient with GPS (dedicated or phone) as backup to check location. That way one can keep GPS/phone turned off most of the time & avoid need for frequent charging.

For long tour where route flexibility is required, tablet might be handy for route planning, perhaps obviating need to carry many map pages.