K-bike,
You have a good point about an electronic device going wrong and shutting off the engine when riding, but just disabling the starter is not the most effective anti theft device. Thieve could push the bike to start it.
On both K bikes, I installed a 30 amps rocker switch under the side panel (The switch could be mounted under the seat and difficult to access if the seat is locked). This switch is shutting off the ground from the battery. The only problem is that each time you shut off the ground, you have to reset the clock. The easy solution would be to pull a dedicated ground from the battery to the clock.
I never use this device for anti-theft purpose even if it could be quite effective.
It's there as a safety device. If I ever get a short and start to see my wiring harness smoking, I could shut off the power in "a flick of a switch"
If you have to get your tool box out and find the 10mm wrench, you may have 1/2 of the bike burned down before disconnecting the battery.
The idea for this switch came after my starter relay burned and even with the ignition switch off, the starter continued turning until the battery didn't have anymore power.
This is a good time to remind people about the starter:
If you try starting your bike with a weak battery, you take a chance to burn your starter relay.
This is easy to understand: Amps = Watts/Volt
The starter is 700 watts, at 13 volts (battery fully charged) it will pull 54 Amps. If the battery is down to 10 volts, the same starter will pull 70 Amps and you have a good chance to burn the contacts of the relay (they will stick together).
The starter will then continue to turn until you disconnect the battery.
During this time, the starter will continue to drag your battery down, and if you get to 6 volts, the amperage will be around 115 amps. You may start to see smoke coming from you electrical tray.
Bert