I'm hesitant to use a killing device with signal loss as the signal loss may be only temporary.

I was flying my Yak on 72mhz with fail safe set to return the throttle to idle. At 150 ft and fortunately level, the throttle went to idle and I checked for elevator and had no control. I sang out, "I've lost it, did someone just turn on?". The person who had, realized it and shut off. By the time signal was regained, the plane was much too far away to have made it back to the field if the engine had quit. In fact recovery was dicey with the plane out far enough where orientation was difficult.

Facts: Had the engine quit from some sort of engine shut down device, the plane would not have been returned safely to the field.

Had I not been using a PCM receiver with fail safe, the controls would likely have gone far over and the plane crashed quickly and I'd not sensed the warning that I'd lost signal control when the engine went to idle. A second or two delay in sensing I'd lost signal would not have allowed time to sing out the problem and get the offender to cut off so as to regain control and have the plane close enough to recover.

Had our field had a proper pin requirement, the offender would likely not have turned on without a pin. I'd lobbied for a pin requirement on 2.4 for those who continued to fly some 72mhz stuff. Instead, it was adopted that all 2.4 users were required to get a pin... and they ignored the requirement and the intent of the pin requirement was lost. That I know of, mine was the only example of a near shoot down because of 2.4/72 mix but our field has seen several 72mhz crashes from failure to extend antenna by those flying both.

Had my fail safe been set up to kill the engine.... the plane would not have been recovered.

Had fail safe not been set to take the throttle to idle, I'd not gotten the early warning of the problem that turned out to be critical in allowing time and space to recover.

No doubt that this is just one scenario and that there are other examples where killing the engine completely was better but until regulations are changed, I'll opt for using a fail safe to go to idle rather than killing the engine.