The defrost specifications are also worth thinking about. Having your heat turn off for a few minutes to do a defrost cycle can be annoying if you only have one unit.
Low temperature means only a couple of degrees higher than ambient. It just constantly radiates. That also mean that heat pump needs to work less hard.
It does require a significant amount of insulation to ensure you don't lose the heat immediately.
And because of the high mass it means that interruptions aren't noticed.
In the north of the country you end up heating your house for some days with resistive heating, but it is still cheaper than any alternative source.