I have been asked several times about throttle kill switches, so am showing you the most common way to set them up and why. This is especially important for Electric aircraft, as an instant start up, when least expected by bumping the throttle stick by accident, is dangerous! There is no momentary switch on the newer Spektrums, so timer starts automatically when you move the stick above 25% and stops when you drop the throttle to zero. I also use my throttle cut switch (H) to prevent my nitro planes and heli's engines from going above idle if I bump the throttle stick by accident. It does not kill the engine. I do that with low throttle trim, but with the kill switch engaged, the engine idles but bumping the throttle stick will not cause it to run up unexpectedly.
This helps.