@richtea999 I don't think that I am (for this route) that sophisticated a user.
I was aiming to get to Bicester and used the app to help (keeping an eye out for traffic, etc) while knowing a couple of the roads that are fun to use. What surprises me is that the app takes a long time to recalculate, even if I am well past the point that "my" route is quicker than the app planned one (here I am assuming it is trying to get to the destination in the shortest time - but is that how the algorithms work?).
Google seems to recalculate much quicker.