I have used all 3 methods, throttle adjusted to help kill the engine, choke servo to activate the choke, and a fiber optic kill switch. I believe if I remember correctly AMA states must be able to kill engine via TX.
All 3 of these methods have worked for me in the past, HOWEVER I have since went with the Fiber Optic due to safety reasons, as with Smart-Fly (which is what I use) monitors the RX and will shut ignition off if there is interference that would result in control loss. I came to this after watching a 35% bird go in at full throttle and was extremely luck it was not in the middle of folks!!!!