If you go gas, don't heed the advice of the guy who says you shouldn't (or at least don't need) an optical engine kill switch. The availability of this device is what really pushed me to try gas in the first place. It is a wonderful safety device. You have at your disposal on your Tx a switch that will kill the engine on demand. Not only is this handy, but in the case of an out of control aircraft, you can kill the engine before it possibly injures someone. If the Rx fails, you will crash, but it will come down with the engine off because without an Rx operating, the kill switch automatically kills the engine. Even a long glitch will trigger most of these devices to stop the engine.

Sure, any device can fail, but failure of the optical switch will normally only cause the engine to quit. I am sure there may be other failure modes and effects, but everyone I know uses them religiously and have not had problems.

A guy at Joe Nall reportedly lost a $6k gasser because he had no kill switch when there was a throttle failure at full power (servo?) He pulled the wings off the plane trying to fly it full out till it ran out of fuel. Some large gassers are just not designed for extended full power flight.