BVF thermostats always include this floor sensor in the packaging. It is worth buying / installing the sensor especially if the type of controller has not been decided yet, but the floor heating system must be laid first. The NTC standard 10kOhm surface sensor is compatible with all BVF brand thermostats and most controllers available in Europe.
The floor sensor is factory-fitted with 3m long, shortenable wires of the same cross-section (resistance measurement must be performed after splicing).