As an update, I've been using this and like it, though to actually get maps to work offline I had to switch off my mobile data. They need to introduce an offline mode.
Clearly there were no live traffic updates but the other significant difference was that only one route was suggested. When online it provides a choice of routes with the relevant ETAs. Here Maps manages to do this offline.
Where Here Maps excels is the speed limit database - it not only displays the current speed & speed limit but also warns (audibly) if the vehicle exceeds the limit beyond a customisable tolerance, even offering different tolerances for city/highway roads. Google doesn't offer this at all and this is why I will continue to use Here Maps as my choice for offline navigation.