Another reason to use a choke servo over idle down is that it gives you a second way to kill the engine. If your throttle servo or linkage fails you have a way to stop the engine, like an optical kill. I actually had that happen to me three weeks ago when a HS-225 (trying to save weight) on my BME yak failed. Instead of flying around until it ran out of gas, I lined up to the run way killed the engine and landed. (I now have a 5925 on the throttle)