In the meantime, I found Heatit Z-Temp 2, which looks like good as well. The only problem is that it does not seem to be supported in OH yet. 
https://www.heatit.com/archived-products/heatit-z-trm2fx/
This one works for me.
The problem with Heatit is partly functioning firmware.
I belive the newer thermostats still have buggy firmware.
My Trmfx2 was not usable out of the box. I had to upgrade the firmware. The fw shipped in the device flooded my zwave network…
Note that Z-trm2fx is an actual thermostat, while I was asking about a control panel, i.e, no wires.
The SRT312 device also looks promising, but I agree that the Danfoss (and also Heatit) devices look better.
Any difference in functionality and/or stability between the two you tested?
Yes, but it should work without any load connected.
Another thing: Im not a fan of integrated temp sensors.
Particulary mains driven ones.
My point is that trm3fx still has trouble with fw.
Hi, want to throw another product in this topic. I also have the same situation with electric heating (ON/OFF etc.) and I controll it through Openhab rules and Homematic switches and battery driven thermostats. Battery lasts more than 6 Months and has an High WAF factor. No complains.
I guess you mean one of the two “Wall thermostats” from here? They surely look good, thanks 
I would mean adding a new system with a new gateway, but they seem to have some interesting devices…
I dont know how the Homematic IP series performs. I still got the older series. Just Homematic. You can also build an gateway with an old raspberry. I got these ones: https://www.google.com/search?q=HomeMatic+HM-TC-IT-WM-W-EU also there is a nice bracket for them to stand on a table or so.
Thanks again, I will check these.
In the meantime, I also found these Zibgee-based thermostats from Salus (I believe they are also being sold under other brands).
While they look nice, I do not see them on the list of supported devices for either the Zigbee addon or the zigbee2mqtt project