The heaters have been built to use only as much power as necessary and thereby not waste energy. They have sponge insulation on one side to prevent heat being lost into the atmosphere. The heat is directed into the optics instead and because of this, less energy is needed to keep your optics moisture free.
The heaters wrap around your objectives, label side out and are held in place by elastic/Velcro attachments.
This strip was used on a Takahashi FS-102 Refractor. It is in excellent shape. $19 plus actual shipping. Payment bay cashiers check, money order, or by PayPal.