I use "Lock on Road" all the time, but on occasions it can catch you out by following the wrong road and making you go off route especcially if their is a road running parallel to the one you want. On one Audax I do every year I get "stung" at a certain point. I'm following the course on a main road and on the Garmin I see that I have to fork right at a junction, which is a narrow lane and down a steep hill, but in reality, the main road (now not on the course) has slightlly gone off to the left, the road that I want forks off to the right (which is on the course), but the little lane off to the right does not show up on the Garmin map and the lock on road has your icon following the main road which is no longer on your course, so you presume the little lane of to your right is the one that you need. I have now wised up to it now after taking the wrong turning a couple of times