Bought a Victorian house a couple of years ago. Previous owner has fitted a Daiken Altherma. It’s a gas combi boiler with a ASHP. So depending on outside temp it will run on ASHP till it gets too cold and then switch to gas. It’s slow to heat up on ASHP, but trick is not too let it get to cold.
ASHP fan is ugly, not as noisy as I thought it would be though. With nothing to compare it too, can’t tell what running costs are like, but it uses ASHP about 80% of time I’d guess. We’d be too cold with just a ASHP though as the old building doesn’t retain heat well.