There's a couple of differences between using a servo on the choke and the optical kill switch. You can set the kill switch so that in the event of radio signal loss, it will kill the engine. Its also solid state, no moving parts to fail such as servo gears and pushrods. Also, cutting the ignition kills the engine instantly - closing the carb can take a few seconds for it to sputter out.
Its personal preference, and I'm sure you will read arguments from both sides of the fence
