Yes, the price is why I've only purchased shelly devices in their sales.
I would agree. One thing to note if going down a DIY route though is to watch out for the Zigbee licensing. There is some talk that it isn't free. Don't know if that is true and whether it makes a difference but worth keeping an eye on. Also, because Zigbee seems to use different embedded processors, you can't just use Arduino programming.
To be honest, if you were looking to fit out a whole house, I would be highly tempted to spend the money on a commercial, integrated system like the Wiser or Evohome. Both of which (and there may now be others) can be integrated to home automation systems. Both of which come with "proper" boiler controllers that work in sync with the TRV's to get the best out of the whole system. They are generally really easy to fit, especially if you already have a standard controller wall plate for your existing boiler controls. In my case (with the Wiser), it was litterally a case of unclipping the old controller and clipping the new one in place.
If you don't go that way, if you are going to fit out many radiators, I'd perhaps get a trial selection of a few different Zigbee TRV's known to be compatible with Zigbee2MQTT. I doubt you could realistically beat the price DIY to be honest as long as you shop around. Get a compatible Zigbee controller dongle and visit Ikea to grab some mains powered Zigbee devices so that you can use them as mesh extenders.
Once you've got your basics set up, I can pretty well guarentee that you won't be wanting to go back to Wi-Fi devices in the future. Of course, with Node-RED and MQTT, that doesn't matter since you can tie everything together anyway as I do across 433MHz, Wi-Fi and Zigbee.
Oh, and I replace the 2xAA batteries in my TRV's about once a year for those devices furthest from the controller (I don't have an extender on my Wiser network). Maybe once every couple of years for those closer to the controller.
One thing to watch out for on TRV's is that the motor torque is sufficient. The Wiser TRV's do sometimes struggle. I find myself occasionally taking one off and doing a full reset and working the pin on the radiator a few times. You would also want to check for noise. Some of the early TRV's I believe were very noisy. I have to say that the Wiser ones are really quiet. So certainly worth getting a few different ones and trialling them if you are going down the independent route.
