There appears to be a small bug: if you select the wrong COM port for machine control, it never times out but the whole thing seizes. After several re-installs, got it figured out by removing the files from the AppData folder.
The tractor spool valve if quite high flow, so my gain is one (1) at the moment, follows line quite nicely, though. Just some hunting when driving over some rough ground, could maybe put a scaling factor into the ino. Dead easy to use with the spool valve lever, put it to float and it’s in auto and then you can use it manually to override and just drop back to float to continue in auto mode.