http://www.amainhobbies.com/product_...ducts_id/27197

That is the one I used - Tower doesn't carry it anymore. It provides both low batt and loss of signal protection. It plugs into rx (one you linked is fine) and then the esc - basically its wired between the rx and the esc. It activates the brake to stop when its triggered, not the throttle servo. You set it up per its instructions and test it to make sure it works. Then just watch for LED - I mounted mine of top of the rx box so I could see it and when my rc would all of a sudden stop, I'd go over and look and see solid red LED which meant loss of signal (interference). I never ran batts down and activated that side of the failsafe (blinking LED).

The failsafe you linked seems to be for nitro and NiCd batts only which would be a practical prob with the preference for NIMH today. It might work fine, but I don't know that either way. You could see if they would answer an email question (Futaba, not Tower) and find out.

Failsafes are disappearing because most radios now have builtin failsafes.