Might be worth it. My dad, who lives in Sault Ste. Marie, MI has had block heaters on various cars for many years. I even installed a couple myself for him. They make a big difference if the car sits out all winter. Starts better and you get heat much quicker.
If you have a garage, don't waste your money. I don't know what Honda dealers get for them but true to form, they are probably overpriced as are all the accessories.