The Surface Range Extender is designed to measure the temperature of a metal surface, and also get maximum radio range (it is a variant of the Pipe Range Extender).
Placing a sensor flat on the metal gives a very good measurement of the surface temperature, but as metal absorbs a lot of the radio frequency (RF) energy, the radio range is severely degraded.
The Surface Range Extender solves this by the use of a range extender embedded in a sensor accessory. The sensor is placed flat on metal, with the range extender lifted up from the metal surface. This design allows the radio waves to propagate better, hence achieving maximum range combined with great thermal coupling to the surface for accurate temperature measurements.