[sgerenser]

I assuming he means insanely more efficient than they used to be, not more efficient than ground-source (awkward wording though). I suppose they can also be described as more efficient in installation time, cost and equipment than ground source, but clearly not in operating efficiency.

[wood_spirit]

Yes air source are really good value in cost effectiveness terms, especially when a house has an existing central heating system they can connect to. But their COP - whilst dramatically improving in the last 10-20 years - is still behind ground source, particularly in the north during winter