Ok, after my runaway board incident here:
I decided that a big dumb almost mechanical cutoff switch was in order.
So I modified Vedder’s anti-spark switch to add a bigger (60A) fuse and some form factor changes and ordered some emergency cutoff switches from Amazon here:
Tonight I wired it all up and tested it - and it works great. Twist the switch to pop it up and turn on the board and mash it to shut it all down.
I’m going to mount this on the rear riser so it is easily accessible while riding. I’ll post some piccies when it’s mounted on the board.