With RC aircraft. we've been doing this since the dawn of time. Nothing special to purchase. You set your low idle on the engine with the TX stick at the lowest point while throttle trim is about midway. Low trim closes the carb. Engine immediately quits.
It's not safe if you don't have a way of being able to kill your engine, no matter what you are operating. On the large gas planes, I run a redundant throttle kill - just in case one system fails.