We could only make this a more controversial topic by adding an Amsoil 100:1 vs Pennzoil 40:1 discussion

I am a big fan of redundant backups since I'm an engineer and understand that a plane is a system depending upon a lot of individual things to all work each time. Many of them won't be seen in a preflight inspection and honestly, almost nobody does a preflight before each and every flight. I've personally seen 3 instances where a ignition kill switch would have prevented a totaled aircraft.

I have one Smart Fly that worked ok for many, many flights. I did experience problems with it one time. Not in flight...just would not allow the engine to start on the ground. It tested fine when pulled from the aircraft. Most likely an end point setting sensitivity or perhaps the fiber optic cable might not have been seated properly in its socket. Nice, with a remote LED, but it is really overkill in my opinion.

The best success I've had is with the $25 RC100 by RCAT Systems. http://rcatsystems.com/electronics/rc100.php I have half a dozen of them and they work very reliably. They are lightweight and cheap. No need to spend $60.