Do the stats work with cast iron radiators?
They only actuate the existing radiator valves so I don't think the type of radiator matters.
You do need valves on which a thermostatic head can be mounted on (with a pin) - see the attached image.
Could you tell us the make/model of that valve?
Also do you know if the Tado Smart TRV fits on to it without an adapter or if one of the included adapters has to be used which one?