bigmandh – the main one you need to change is the automatic recalculation, as otherwise in, for example, a circular route, it will either try to take you to the end of the route immediately, or just think you’ve completed the route as soon as you set off!
hebden – IMO it would be fine for that, and i frequently have used mine for just those type and length of rides, it is more that it is temperamental in use! Kind of hard to explain until you use one, but I have used mine for 1,000s of miles of riding, including London to Paris and I have survived so far!