I’d disagree with these points. We have a GSHP and I’d say you definitely need a specialist to spec it all up. Ours runs radiators which we had to update and they ran fine, though recently we upgraded them to more effective rads built for GSHP specifically (which are awesome, so far). The radiators do not get as hot as standard rads, but our system is set up so that on a very cold day the temp of the system goes up accordingly. Our rooms do get toasty warm, but it’s all about efficiency and getting the right spec. I will say though, that it’s taken a few years to get it all running smoothly with no hiccups (touch wood), and we got the grants when installed which will virtually cover the full install when all said and done, and finally I also had the old LPG boiler set up as a backup (never needed it yet - touch wood).
Finding a good specialist in these is hard though. You want the reliable backup when something goes wrong (as it inevitably will at some point) and a lot of plumbers will not have much experience of them.
And yes they are noisy (or ours is at least) and that’s why it’s in the garage across from the house.
They won’t be for everyone. Nowadays, and after having a few put in upstairs, I would definitely look at aircon units that would also warm up the rooms - very efficient units nowadays.