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Monster1985
If anyone's looking to go with Octopus/British Gas, they mostly offer Daikin ASHP units. Something to be aware of is the propensity to oversize the Daikin units based on overstated heat loss calcs.
Oversizing is not so much an issue with Vaillant ASHPs due to their 'energy integral' control mechanism and good modulation range, but with the Daikin Altherma 3 range there are only two actual sizes, with artificial software maximum power limitation to make up the in-between models.
The 9kW - 16kW are the same unit, same for the 4kW - 8kW range.
The minimum modulation of each of the two flavours of unit is the same, meaning that for most of the year when your house's heat demand is low, the 9kW model that Octopus/BG love to install "to be on the safe side" can't modulate down below ~4kW of heat output, which is way too much for most properties. This is because it is, in fact, a 16kW beast with a software limiter.
What this practically means is that the unit will cycle drastically, causing high compressor wear, yoyoing internal temps, low efficiency and high electricity consumption. The 8kW and below have a much lower minimum modulation level, and are much more suitable for the average house.
If you get offered a 9kW unit (or above), make sure to question it, and ideally get an independent heat loss survey done, or do your own on the Heatpunk website or similar.