BadlyWiredDog - MemberAh - SatSynch was the bit that was missing.
It's still clunky on the device itself, you really need to use with a map and it's still not ideal, but the SatSynch software for PC and Mac now works fine, so online route planning and transfer a GPX file over is the way to go.
Is the OS mapping actually necessary?There are definitely times when it's useful. Having been weaned on a Garmin Geko (sans mapping) I can think of situation where a number of tracks have all split out from one junction and it can be difficult to determine just which left track one is to travel along, sometimes necessitating a retreat. Reference to a map can resolve this PDQ. My old Geko has seen better days and I'm considering the alternatives.
The other point to make is that navigational errors made while cycling tend to escalate fairly rapidly. Discovering you've gone up the wrong path while walking, you're unlikely to have to retreat more than 100metres or so. On a bike, with the head down and going down a nice descent, it's a bit dis-heartening to find you're gonna have to push/ride back up again

