Correct it uses the rear defroster button to essentially activate the factory LED's so if you are out at night at a cruise night or whatever driving you can turn them on and off without having to open and close the trunk.
DO we need this not on your life, would we be better off having it - likely not
but for 100 bucks essentially you can decide if you want them on or off. The reviews I have read cover off concerns like the glass might get too hot since the rear defroster is on now - no issues whatsoever - but others have said just unplug the rear defroster at the glass which is an easy fix. I have never used the rear defroster since I picked up my car.
If i can buy it within Canada even better but if not that's okay too.