heat pump are highly inefficient if outside temp gets below ~5 degC and that's what happening right now on most of Europe ( incl. southern europe, I saw spain mentionned here ... )
Standard heat pumps these days work great even at 5C, at least any one that I have seen.
The H2i line from Mitsubishi maintains 76% of its COP down to -25C (-13F).
It should be the same in Europe and it will work in case the temp drops too low.