It seems a bit more sophisticated than just a flasher, which would flash your brake lights steadily on and off, like a turn signal.
With this device, your brake lights would go "blink-blink-blink-blink" rapidly, then revert to steady on for 3.5 seconds, and then cycle through again.
Here's how it's described:
"Maximize your Brake Light Effectiveness with BackOFF. This compact solid state electronic module converts ordinary brake lights into an attention getting "wake up" and "get off the cell phone" alerting device, creating more visibility when braking or stopped. With BackOFF installed your brake lights will automatically flash on/off 4 times, followed by "steady on" for 3.5 seconds. This sequence automatically repeats itself as long as the brakes are applied. This pattern is not random, but has been selected because of its ability to gain and retain following drivers attention."