My landlord has fitted all heating radiators with electronic thermostats, namely the Honeywell Rondostat. They can be programmed with two temperatures (cold and warm) and two time intervals per day where it should be on the warm temperature. Usually one does weekdays in the morning and evening, and weekend from morning until nighttime. They measure the temperature and adjust the valve accordingly.
This is quite nice and likely saves a lot of heating. Most importantly one can just come home and find the rooms to be in the warm or cold setting that one wants.
These things have two major drawbacks though: Open window detection and batteries. The automatic detection of open windows sounds quite nice, just open the window and the very cold air will tell the thermostat to shut off. In reality I let it turn off a few minutes before I open the windows. And when I have closed them, I want it to start heating right away. But it usually won't let me, assuming that the window is still open because it is so cold now. Basically one has to wait five minutes before it starts heating again. Good intentions, but it actually hurts more than just doing nothing special would.
And then the batteries that are eventually empty. Just by mechanics it takes more torque to close the valve than opening it. One can even hear how the motor has a lower angular velocity when it closes it, with a lower pitch sound. The higher torque means that the motor draws more current from the battery, such that the voltage drops. Sometimes it drops below the voltage needed to support the electronics. In these moments the thermostat will just die and eventually recover. However, it lost its state and will ask for the current date and time. It will have forgotten that the valve still needs to be closed. Then the room will heat up and the thermostat will not act.
This is especially bad in summer because the thermostat has one additional feature that is meant to prevent the valve from getting stuck. Every couple of months the thermostat therefore cycles the valve by completely opening it and completely closing it. Often in the summer the battieres are already rather drained from the winter and the additional idling for months do not help either. Then it opens the valve completely and fails to close it. I usually notice because some room is ridicolously warm. And occasionally this happens in my bedroom and I wake up with a giant head ache from dehydration.
Independent of this they are smart, but not really. There is no way to work with them remotely, and one has to program each room independently by twisting the dial and pressing the buttons. This of course makes it independent of a cloud or central server, and also one cannot attack them. Yet they take a lot of setup, especially if one had several radiators in the same room.
I am not sure, but at this point I think that I prefer regular analog thermostats that are just reliable.