MOTO-D Racing Dual-Temp Tire Warmers

[GM Man]

Tried doing the search thing, but didnt come up with these, so hopefully they havent been covered before. Anyways just curious has anyone used these before? Are they junk or do they seem to work well?

http://motodracing.com/accessories.html#ecwid:category=460812&mode=product&product=7507110

Thanks...