I have a Facet electric fuel pump, and as much as I'd like to install a safety switch, I do wonder if either of these options will really do the job.
The pressure switches I've seen all seem to be set to turn on around 5-10 psi. The BE oil pressure can drop close to this level on hot days, at idle, and I'm concerned that the switch might shut off the engine under those conditions. Another concern--suppose the car sits for a while and the fuel level in the float bowl drops. How do you start the car? Until it's running, the fuel pump won't operate, but you need to have it running to refill the carbs. Maybe cranking will raise the pressure enough to turn the switch on, but even then you'll need to crank it a lot.
As for the inertial switch--there are a lot of variables that the manufacturer doesn't tell you about. How much inertia does it require, and from what direction? Would it work for a side or rear impact or just front? Will hitting a pothole trip it?
My solution, when I get a chance to do it, will be an electronic circuit that senses when the engine is running, from the ignition coil voltage, and turns the pump on. It will have an override so that the pump is turned on for, say, 20 seconds as soon as the ignition switch is turned on.