Sorry if I missed it here in the thread, but another alternative exists... putting a servo on the choke and using the choke to, well, choke the engine. I have put it on my latest DLE55 engine... I had an old servo laying around... works fine.

I have had the runaway bird situation before, the idle changed as the engine warmed up in the air and it was impossible to land. I solved it by removing the low idle restriction SCREW from the engine and setting throttle servo end points to allow killing engine with the throttle. I am very careful now with throttle setup before flying. I do not see how it is possible for an engine to continue running when the throttle is fully closed. My problem was the screw prevented it and left a small air opening.

I don't have any ignition kill switches, but have considered getting them. This discussion will have influenced that decision. I like to fly as safely as possible, but I do not wear a belt and suspenders either.