I have used VThermo for a week now and generally it works perfect for zones.
In a large room/zone where the temp sensor in it self gives a slow/delayed measure VThermo still has a delay of triggering the heating.
It seems that hystereisis has a built in minimum of approx. 0.5 C even if the hysteresis setting is set to 0.
It would be good, at least to me, if the hysteresis could be set and used as 0.