My quarter scale Decathlon used a magneto ignition with a micro switch mounted n the engine bay. A non-metallic push rod actuated tot he switch to short the magneto to ground. Any ignition noise was thus kept in the engine bay. That engine is now being converted to electronic ignition and the same system will be used except the NO contacts will be used to kill the igntion rather than the NC. That system is as reliable as the servo and radio system that operates it. That radio system is entrusted with the flight of the airplane so it is equally good to kill the engine.