You can add up to 25 rooms, but only 10 rooms can actively call for heat from the zone controller. Tado have previously communicated that the 10 room limit is not going to change.
@Yogenp Yes. IIRC the limit is 10 zones and 25 devices (we have 10 zones and 13 devices for 12 rooms). If you have more than one rad in the room (a zone), they are grouped in the room. E.g.1 we have two rads with SRVs on the 'landing' and the zone controller is the 'wireless receiver'. E.g.2 You can also assign the room 'zone' setting as 'independent', which means that the SRV will act like a typical TRV and not call for heat. We have the loo and one bedroom as 'not assigned', both with independent room temperatures.