The installed correctly part is part of the problem. Heat pump based heating systems run at a much lower temperature so usually you need to have new bigger radiators installed, which would add to the cost, and adds chance of needing to have all your floors ripped up to replace the heating pipework (although I suppose that's also possible when replacing a gas boiler with a new gas boiler). You will potentially need to make sure your house's insulation is actually doing a reasonable job which to be fair something that you'll really want to sort regardless of heating system, but is a bit more critical with heat pumps. So can be pretty costly to get installed in an existing property (especially if you've got a house built with solid walls which to add insulation might have to be done internally), but hopefully they continue to install them as standard in new builds. I know down here in Cornwall the local council had banned new builds with gas heating (not sure if that got reversed or not).

I would be pretty tempted to switch mine over to a heat pump from gas, but the big issue for me is where to put the external unit, I think to meet the spacing requirements I'd need to pave over more of my garden or move my back gate further along the brick wall it's in.

I can see some similarities with the EV hate as well, where a lot of people have complaints based on the early generations ignoring the fact that technology has improved in the years since. There was and I assumed still is a relatively small amount of plumbers who fully understand heat pump systems, and how they should be installed, configured and used. Someone at work has a reasonably new build has heat pump and they weren't able to find anyone local who could service them, so basically the whole street clubbed together to get someone from further away, but other than that they have loved it. I think I remember reading somewhere one of the common problems was people running the boost electrical heater pretty much constantly which of course costs a fortune to run and is normally designed to only be used when it's too cold outside for the system to work normally.

I'd consider a ground source one, but don't really have enough space to install the horizontal one, and given the old mine shafts in the area I'd be a bit worried about getting someone to drill some bore holes for the vertical ones.