I have 2 such devices. They may not be suitable as the only source of heating, but they are ideal for supporting the normal heating in winter or as the only heating during the transitional period. One room is about 18m2, the other 42m2 and both are high rooms with sloping ceilings. I am very satisfied with the Dyson Hot Cool.

I bought this unit only in summer and used it to "cool" the bedroom 16m2. It is pleasantly quiet and does the job on warm summer nights. I briefly tested the heating function once and was surprised how much the unit heats.