Control devices (regulators), which regulate carbon-copper polymer film heating are very different. Right choice of regulator significantly affects amount of electricity consumed (i.e., your money).
There are regulators which you can define desired room temperature only. It means that carbon-copper polymer film reaches its maximum temperature, which is maintained until room temperature reaches the desired value. First, room temperature depends on outer conditions, and it is not always possible to reach. Second, the film is always heated to the maximum acceptable limit. It would be equal to walking on hot beach sand, plus, we cannot talk about reasonable use of electricity here.
Regulators of other type provide control of floor temperature. Heating is switched off once floor temperature reaches your setting, or floor heating is automatically switched off when temperature exceeds the acceptable. This solution is safer, but still, such parameter of interest for you as desired room temperature is ignored here.
Regulators of the third type both respect: air and floor. These devices are usually made as computerized embedded systems, which provide for programming individual heating modes for different day-night periods.
Carbon-copper polymer film usage quality depends on quality of regulating device – thermal regulator (thermostat) – operation. Regulator consists of two parts: control and commutation units. Operation of control block (power connection/disconnection modes) is defined by programmed algorithms, and commutation unit connects/disconnects power according to commands received from control unit. As commutation device serves mostly electro-mechanical relay, which, in accordance with voltage level on control contacts connects/disconnects power contacts. Micro-sparking and gradual contact wear takes place during contact connection and influences life cycle of regulator. As a result of repeated switching sparking and sometimes even contact adhesion may happen. If heating device is not connected to the automatic fuse, consequences could be sad.
You should not trust unverified solutions even if they have all certifications, which, unfortunately, does not confirm quality of control unit operation algorithms.