Personally I am a big fan of optical kills. I am not a fan of flying around for 25+ mins at 1/2 throttle because I lost a throttle servo or because a muffler came loose and I couldn't get the idle down far enough. Things happen and being able to kill your engine any time you want is just handy. Required? No, but I would rather spend money on that then a manual switch, I think it's more useful. Let's not forget with a radio or battery problem it kills your engine automatically, a manual switch doesnt.

As far as flipping a switch, well that's your own fault. If your radio has dials put it on a dial. If you don't have dials put it on a switch you don't use very often and that is out of the way. Always show anyone who flies your plane where the kill is so it's not hit by mistake, if they hit it, they didn't listen but if you are letting someone fly your plane I would hope they fly as good or better than you.