I am thinking of the more basic air/air units rather than this air/water.

One well placed air/air can reduce the need for direct electricity heating a lot, even though some might be needed to assist in a bedroom or so.

My parents installed a air/air unit in the middle of the house (180kvm) for $2.5k this summer and it keeps the whole house heated except one bedroom that needs some assistance from a radiator.

That's about the same size as my house... I also have a air-to-air heater but don't even use it because the central heating is more than enough. But interesting to know it could actually manage almost the whole house if I need it!

I have an earlier version of this and they're great, although they use the heater more than the heat pump in winter so bills are cheaper but not miraculously so. The newer versions like your have a bigger compressor, which I think gives them a substantial improvement.

The main problem I've found is now that it's getting old and having problems there's nobody in my area that knows how to maintain them, they only install and then suggest buying a new one when the old one needs new parts, which is frustrating and in line with most white goods these days. So advice for the future is that forums like byggahus.se are good for advice on trouble shooting & parts replacements once it gets old enough to have problems.

I had a Nibe 640P before this. It had broken down almost every year for some 5 years before it finally gave up this year: it started leaking, several parts were not working anymore according to the technician and according to him, they couldn't even buy anymore some of the parts (the machine was only about 15 years old!)... so I didn't have a choice but to replace it... the previous times I fixed it cost me between 4K and 10K SEK (change of some electrical component or sensor that broke, replacement of the actual ventilator a couple of times)... If I could keep fixing it reliably I probably would... but these days, after 15 years every technology changed so much that what you've got becomes a museum piece that can't be fixed. Same thing happened at almost the same time to my alarm system :( Sektor Alarm didn't even offer to fix it up... it was using 2G which apparently is slowly dying in Sweden. At least they got me a very good discount and I spent "only" about 5k SEK to get a very modern alarm system with cameras, vibration sensor, mobile app and bells and whistles :). But again, I'd rather just keep what was working if I could as to me it feels like a huge waste to throw away so many electronic components which are mostly working just fine... however, you just can't do it anymore.

Yep, 15 years was what I was told was the life expectancy of the system and nobody is interested in making them last longer. I try to fix things but as you say, finding spare parts is really difficult.

Retrofitting floor heating might be very expensive though? Especially in some older houses

When I bought the house, it already had floor heating across the entire plan... but from what I see, it's not that hard to DIY if you're so inclined. Specially with floors like are typical in Sweden, it's like laminated flat boards that are easy to replace: https://www.bauhaus.se/hpl-laminatgolv-berryalloc-ek-vitolja...

It looks pretty good too... you need to do some cutouts for the warming pipes underneath, there's lots of Youtube videos showing how :D

But luckily, my floor heating apparently is still in very good condition so it will be a while before I have to replace that.

The floor heating itself isn't that expensive, the problem is you need to redo you floor, which sometimes means destroying it and doing a new install. We wanted a new floor anyway so not a problem, but if you have something expensive it will add up.