We currently have IMI Theromstatic units installed on all our radiators. Photos are attached. Will I be able to replace the unit heads with the Tado smart radiator thermostats or will have to replace all the valves with conventional ones?
These valves are thermostatic, so you should be able to control them (please see the note below).
As per the pictures I can't see clearly if they may be M28x1.5 or M30x1.5 (that's about the diameter, 28 mm or 30 mm). If they are 28, the adapter is included, and if they are 30, it's the thread size of our Smart Radiator Thermostats.
However, the valve model seems a bit too tall, and it could be that even being on this size range, the Smart Radiator Thermostat couldn't reach the thread to be mounted (and then maybe you need a different adapter or replacing the valve if you may). Unfortunately we couldn't know this for sure unless you try to mount it.