In reply to MeMeMe:
I've not got experience of them in a small domestic setting but have been specifying them for non-domestic and multiresidentual a lot in the last few years.
There has been a tipping point with the decarbonisation of the grid due to renewables leading to heat pumps now being lower carbon than natural gas boilers. If you have a focus on carbon and local air quality they are a good choice.
If you have access to natural gas it still works out a little cheaper to use that but if you are off the gas grid I'm sure it's cheaper than oil, batch purchase ofoof gas or electric panel heaters.
If you then sign up to a fully green energy tariff you can be zero carbon.
The ability to generate large amounts of domestic hot water using them is limited and if you are a big user (large family) that might be something to consider.
It is also vitally important to get them appropriately sized. Their efficiency can collapse if they are worked too hard. Also watch out the method you use them. There are products that are highly effective when running 24h day which are outrageously expensive if used traditionally with on off periods.
Post edited at 14:07