Well, it's only $10 bucks, but I myself wouldn't get one. Never needed one before, don't need one now. It looks as if the point of it all is to avoid runaways...if I were you I'd just get a failsafe that will kill the throttle and apply the brakes if your reciever batteries get low.
It is to alert you to any radio system problems, from low battery voltage to glitching and interference. It magnifies any interference to alert the operator, it is a unique piece of equipment and is unlike the normal failsafe that most people use.