* How would the heat be moved around the house?
* Obtaining permission to modify the exterior of a multi-occupancy dwelling is extremely difficult.
* You'd still require a source of hot water, reducing the already small savings over an efficient combi-boiler.
Based on the estimated savings of the Energy Saving Trust, it'd take around 26 years to pay off a £3k install that replaces a modern combi-boiler[0] and that's without the cost of using electricity to provide heated water. As recently as March of this year Which claimed most houses would have paid an extra £80/year if running a heat pump[1].
They could be a good choice for completely new installs and people stuck on resistive electric heating if they can find a way to disperse the heat evenly. I'd bet a lot of money that the majority of properties with electric heating are rentals, good luck convincing a landlord to pay for anything.
[0] https://energysavingtrust.org.uk/advice/air-source-heat-pump... [1] https://www.which.co.uk/reviews/ground-and-air-source-heat-p...
Moving the heat around the house requires doors to be open and thoughtful placement of the head units which have fans in them to push the air around. It is certainly not ideal but we are comfortable.
And yeah, cooling is not a thing in the UK, my point is folks are definitely going to be looking toward that given the summers people have been having, increase heating costs will make mini splits a double win. No brainer to me and I bet mini splits will be in limited supply this summer in Europe.