Programmable thermostats allow you to control the room temperature. They are easy to add to an existing installation. In some cases, they can even be controlled with an app. The solution is mainly suited to existing buildings.
A complete smart home system gives you much more extensive and simpler control options on the heat generator itself. The energy savings are also significantly higher as a result, since this control directly influences the amount of heat produced by your heating system. In contrast, programmable thermostats only control how much heat flows through the respective radiator.
In other words, if your goal is to save energy, there are more effective methods than intelligent heating thermostats. Either a installing a system that directly controls your central heat generation or – in the case of outdated, inefficient heating systems – replacing the appliance itself.