Hey Goirish
LOTS of commentary on do you need one or not. ALL points of view are valid on both sides of the discussion.

Listed are options for killing your engine safely.
1. Servo on choke plate. The reason is for easy of starting, but also for stopping the engine either at the flight line or if you experience a throttle related issue in the air.
2. REMOVE the idle stop screw. This will assure that the carb throttle plate will close all the way and that this bolt will NOT vibrate its way down in time giving you a higher than needed idle. This trick is used by many modelers. In fact, I will be updating my manuals with this item.
3. Use another servo to mechanically turn off your ignition switch.
4. Use an Ignition kill switch.

and of course the FINAL SOLUTION

5. Dump the plane and hope for the best.... It is called DOWN elevator solution.

Many modelers use the KISS method. The simpler the wiring the less chance for problems. Again... extremely valid methodology and thought.
Personally... I advocate the use of ignition kill switches because of that possible one in a million chance that a situation will occur that may cause injury to people and to lesser extent property. I call it my "peace of mind" policy. And for me.. it is worth the small cost of the switch!

Cheers
Henry