If the PC goes haywire, no big deal. You just unplug the cable that goes to the PC, plug it into a manual override box, and you have discrete control of all the circuits. It takes a little more to hotwire the car than the override box (intentionally), the EFI won't work unless you know how to enable it.
I don't let the PC control critical functions that could stall the car while in operation or create a hazard condition like no headlights for example. Things like fuel pump power, EFI power, headlights etc are either powered by the manual power switch or under hardware control (they latch on until main power has been removed). The PC can go completely haywire and the worst thing that happens is you lose the dash display and the ability to restart the car (once you manually power it off). To limp home, you need to perform a manual override, and essentially hotwire the EFI. I'm the only one that drives the car and I could get it into limp home mode within a minute or two...no big deal.
It's as safe as a cobra gets.
