Note that the only really effective failsafes are the ones built into PCM receivers. OK, maybe not so relevant to a featherweight perhaps, but I would not consider operating a heavyweight without PCM.

All an external failsafe can do is check that the signal is within a valid range. If you get some interferance, but the bad signal is still within range, then the failsafe will happily let it through, firing the axe or whatever. Next to useless.

A PCM reviever can generally detect that the signal is invalid and block it.