Thank’s for the tip! Ordered two of them. 
I also ordered 2 and installed one already. Anyone knows what all these fields are?
occupied_heating_setpoint: 21
unoccupied_heating_setpoint: 16
pi_heating_demand: 76
eurotronic_system_mode: 1
eurotronic_error_status: 0
How to change the occupied/unoccupied heating? Are these states the on/off state of the climate entity? For now I just keep it set to Heat and change the setpoint temperature.
This is a nice thread. Would love to know about what things worked for other people.
(maybe instead I should create a new thread?)
I went with Homematic and didn’t regret it one bit.
When I see what others have to go through with Z-wave or Zigbee, I am really glad I went with a solution which works out-of-the-box reliably and which could be easily extended.