That's correct, motor failure is rare, however prop failure can happen, flying off leaving you with only 3 props on a phantom. I think this occurs when pilots get in a hurry to fly, which I'm guilty off, I'm always in a hurry. I always double check my props, yanking on them good. I've seen several videos of props flying off, but cannot recall any motor failures. The next possible failure is ESC failure, which usually happens on hot days and long stressed flights, like climbing a mountain, full up and forward for extended times, or the internal fan fails.
Even though all of these failure modes are possible with Phantom, and could be mitigated with a TH craft, I still wouldn't consider owning a TH because of the lack of sophisticated software from Yuneec, and the inability to easily backpack the craft, as well as the long setup time, reconnect times during flight (since they use wifi), and mediocre range capability. IMO any drone that can't perform like Lightbridge (range wise) is unacceptable, but that's me.
