I'm a newby gas guy, but my first 50 size has the fiber optic kill switch, and the 100 powered 33% Edge I'm building now will also have it.

You'll get a number of answers about this, but IMHO a kill switch is just a really good idea. I think that if you're building something that size, the extra for the kill switch is nothing for the safety factor it offers. Mine are setup, and I test them to assure that in normal circumstances it works, so that closing the throttle will kill the engine. Then I add the kill switch to the same switch on my transmitter that I've used since I started flying glow stuff, which closes the throttle and activates the switch on channel 9 of the receiver.

Use which ever switch you've been using so far to avoid confusion.

Even though most modern ignition modules will shut off after a certain period of time where the trigger has not passed the sensor, if the radio is off, there's no power to the ignition so I figure there's an extra safety factor there as well.