If you have your own boiler you will need the wall thermostat to turn the boiler/pump/valves on and off. Also, if you have stored hot water and are considering the extension kit then you must have a wall thermostat in the system.
You can disable the wall thermostat as a measuring device and leave it just to switch the boiler on/off. However, if you have a wall thermostat and a TRV in the same room then it is probably better to disable the TRV as a measuring device and use the wall thermostat to read the room temperature.
"If you have your own boiler you will need the wall thermostat to turn the boiler/pump/valves on and off."
Why do you need a wall thermostat to turn the boiler on and off? Surely that's the whole point of a specific TRV doing a call for heat on demand. Otherwise, you would have to set the wall thermostat to the same temperature as each room.
My wall thermostat failed a few weeks ago and I've been running with TRVs alone since. I am in the process of replacing the wall thermostat though because of the increased accuracy in measurement, not because the heating stopped working.
The boiler needs a call for heat to fire up the burner, switch on the pump and to open the motorised valve for hot water to flow to the radiators.
The wall thermostat is linked to the boiler using the relay method or a digital bus to call for heat. As the TRVs cannot communicate directly with the boiler they talk to the wall thermostat to make the call for heat on their behalf. The TRV will then open so that hot water flows through the radiator.
The Tado TRVs don't communicate with the Smart Thermostat in my case. They communicate with the extension kit, which is connected to the boiler controls. The Smart Thermostat is wireless.
As mentioned, I have been using Tado TRVs without a Smart Thermostat for almost a month now since my thermostat broke.
You have a different setup to @Coyoteblue as you use the extension kit as the interface to your boiler. Without the hot water controller the wall thermostat has to be the interface between the valves and the boiler.
If you are happy with the temperature control provided by the TRVs then yes, you could dispense with the wall thermostat.