I use a tomtom rider which is great for day to day navigation on the street and the winding roads function works brilliantly!
For off-road use it's pretty much useless since you can only plan a route by setting via points and it will calculate the route between them over normal roads.
The original software for planning is also quite rubbish, but I did find a brilliant website to make (on-road) routes extremely easily.
It allows you to set the beginning and end points and just drag the route where you want to go.
You can export the route with a few clicks directly to the tomtom device.
If the route shows differently on the device, than just ad some more via points.
It uses Google maps and is free!
If you're doing more than 10% off road riding I think something like the Garmin Montana would be better.
For day-to-day navigation the tomtom rider works a bit better than the Garmins I've used.
Ps. I've used a trippy GPS for an off road ride a couple of months ago and that worked brilliantly.
It gives you road book style icons for navigation, but the newer ones can do normal navigation as well I'm told.