You can retrace tracks, spot lock, and autopilot from ipilot.
I pilot link does everything that you can do with I pilot plus more. Ipilot link allows you to link your trolling motor to certain hummingbird graphs. You can then control your tm from the graph to follow a specific contour or even troll at a specific offset to that contour. You can tell the trolling motor to go to waypoints on your graph. You can adjust tm speed from your graph. Hope this helps.