Great post. Thanks for sharing. Could you name the manufacturers, as it might help others in their decision making?
There are 2 heat pump trade associations worth checking out: https://www.gshp.org.uk/ - mainly Ground Source related but a good selection of installer members, and useful background info https://www.heatpumps.org.uk/ - most of the main manufacturers belong the this assoc, a little more emphasis on air source.
One thing to consider when selecting an installer, is that most manufacturers will offer an extended warranty if you use one of their accredited installers. This incentivises installers to keep up to date with training etc, and should provide greater confidence for customers - most manufacturers will offer a search function or connect you with a local installer via their customer service team
There’s still a lot of confusion about heat pumps, but the tech is well proven. The current weakness is at the system design stage, so make sure you get a decent installer on board, with a track record recognised by the manufacturer.