Hi, I've just bought a Dakota 20 with gbdiscoverer map of the South East and Wales (1:50,000 – same as OS Landranger).
For the route planning, I'm trying Quo by Mapyx(www.mapyx.com). The software is free, you have to pay a nominal sum for paper maps, and then you get the e-maps free. I'm finding Quo is a bit slow and glitchy, but it is very cheap and the support is good. It may well be that it's me who is bad at Quo, rather than Quo being at fault.
I haven't tried OpenStreetMap, or any of the others. I've only had it all a couple of days and I'm going to give Mapyx a longer trial because, as I say, it may well be that it's me whose rubbish rather than the software!