Yes, you can use the Smart Thermostat and Smart Radiator Thermostats in your bathroom. However, take care to install your tado° devices in a spot where they are not directly exposed to water splashes.
They should be installed at least 2.25 m away from the bath or shower, and, at least, 0.6 m away from your washbasin.*
*The Smart Thermostat has an IP30 rating and the Smart Radiator Thermostat has an IP20 rating.