phone navigation - are there any real differences between apps

[chilswelluk]

I have no experience of navigation on a phone, but I realise there are zillions of navigation apps available. But my question is are there any real fundamental differences in functionality between the apps?

I understand that each app will use a slightly different GUI, but won't the underlying map data be the same? Presumably all of them use either google maps or openstreetmap (with the exception of maps for walkers)? And I guess the ones that use openstreetmap may have an option to load your own custom map tiles, or load maps on a country by country basis? I guess some of them also support navigating with georeferenced images. But really are there any fundamental differences between the various navigation apps for phones? Am I missing something?