I use room thermostat to, but seems its not help. I think its possible that heat pump will be
working more effective(i tell about power consuption) if its working at minimum power but for a long time then if at full power short time. I think thats possible with installers options, but I didnt understood how, til now.
I bougt it on Climaway site for 3100 euro, but I think that its not actual for You, becouse I saw similar price in UK. Room thermostat bought on Ebay, HWT thermostat from China - for reasonable price. Pump connected to grid with soonof wifi module, its counting energy consuption.