It is not a good idea to fit TRVs to your bathroom radiator, simply because the TRV will not work properly.
TRVs have their own thermostat to control the temperature of the room. So, the heat caused from having a hot shower or bath can confuse the TRV or shut it down completely.
Not ideal if you were hoping to get wrapped up in a nice warm towel!
For more information on TRVs, check out our Thermostatic Radiator Valve Guide.