We don’t tend to use air/air heat pump systems in the UK, even for new builds, always air/water.
Because of lower water temperature output of heat pumps compared to the gas boilers they replace, usually you need to increase the size of radiators to be able to achieve a room temperature change in a reasonable time. What is being referred to as efficiently, is actually just a measure of performance of the radiator, not actual energy efficiency.
I recently replaced the heating element in my delonghi coffee machine, and was also surprised to see how wild it was inside