You make a good point.  I can see how it would work OK on a tractor.  On our sprayer, we are turning around at a pretty good clip and going 20 mph by the time we hit the end of the headland.  It doesn't give you much time to get perfectly lined up.  Sometimes you think you are lined up but it doesn't take over.  By the time you realize it, you are 5 ft off.  If you aren't using the steering column switch, you can continue to steer until you are 100% certain the edrive has taken over.

If you are using edrive on a tractor, I think the steering column switch would work OK with the auto engage feature.