Alexa is Amazon not Google. Wiser works wirh Alexa and Google Assistant.
You do need Wiser TRVs though. Let's say you have a room thermostat in the living room set to 22 degrees and this is reached. The room thermostat will not tell the central controller to call for heat. However, it cannot turn off the radiator so if another thermostat is calling for heat, water will also flow through the living room radiator even though the room has reached the desired temperature.
TRVs are a must have as far as I am concerned. Room thermostats are desirable as it allows the temperature to be measured in the location you want rather than right next to the radiator. If you have multiple radiators in a room a room thermostat controls both radiators.
I have TRVs in every room (except for the bathroom) - 11 in total with 3 room thermostats.
Hope this isn't too late to help you decide.