im running the platinum 4800 without a cutoff for several months now with no problems
once the car slows, i pick it up and charge the battery. unlike nimh or nicd's, you cannot run the pack down to a crawl. once the car slows down, stop immediately and pick up the car.
those lipo cutoff devices you mentioned are good safety nets to prevent overdischarging
i havent used one yet but i think once the cutoff kicks in, you cant run your car anymore. unlike using lipo without cutoff, you can still crawl the car which will likely cause overdischarging of the lipo.