Since we are on the subject and this very topic has been going through my mind a lot recently. I gotta say I don't think the Chicken Hawk stuff is all that great. Best known maybe and sure they have some decent customer service which is more of a rarity in this day & age, but in the grand scheme of tire warmers they are not my first choice. I currently own 5 sets of tire warmers from various brands and I have owned at least a dozen more since the mid-90's and have sold quite a few to customers as well and my favorites are the Woodcraft. I don't know if they outsource them or make them themselves etc, but in my experience the Woodcraft warmers take more abuse for a longer time than any other brand on the market without failure.
The worst by far were the Bikers-Lab. They became unusable within 2 days at the track.