I had a Garmin nuvi and as silverburn says it's routes are quite often stupid...

It would often try to do things like take you off a motorway and drive through a town and then bring you back on to the motorway at the next junction... or take you down farm tracks rather than a main road.

You also couldn't edit or save routes, the most you could do was add waypoints, but would have to re do them every time you repeated the journey which is a bit annoying.

As soon as I had an android phone I changed to CoPilot for less than it would have cost to upgrade my Garmin maps.