Clivet is, I believe, Midea rebadged.  There are several on here with Midea heat pumps who may be able to comment.  They are not the most advanced in terms of control or noise reduction, but so far as I am aware otherwise sound.

Noise levels vary quite a bit whether monobloc or split, so best check manufacturers specs.  Note that noise POWER (not noise pressure) is the figure to compare, generally in the range 55-65dB or thereabouts.  Noise can be a problem but with sensible siting and a reasonably low noise pump is unlikely to be.  With a split the compressor is likely to be indoors, you need to think about the siting of the indoor unit if it is - there are two parts of a heat pump that make noise, the fan and the compressor.  The fan will always be outdoors of course.

All heat pumps are dependent on a solid design of the rest of the installation, get this wrong, as some installers (at least in the UK) do, and you will end up with poor performance.  The best systems in the vast majority of domestic cases are the simplest, where the heat pump is connected to the emitters with no intervening buffer tank, low loss header or heat exchanger, and then run on pure weather compensation with no TRVs (or TRVs in a minority of the rooms) and no external controls like smart stats etc. which can mess up the performance of a heat pump big time.   The other thing to get right is capacity (measured in kW).  You want to right-size heat pumps not oversize them seriously.  This means determining the house loss which can be tricky.  In the UK some installers seriously oversize more or less habitually, again leading to poor performance.

Depending on where you are in Italy you might want to consider a system that is also capable of cooling.  Almost all heat pumps can cool, some require additional hardware to do so (eg Vaillant which requires a rip-off coding plug that sells in the UK for £400, but is in fact just a resistor worth less than 1p!).  The emitters need to be suitable.  Radiators generally wont work, UFH or fancoils will.  Italy seems to have the largest selection of fancoils, including some very swanky designer models (with some equally swanky prices), so you are in luck if you go this route.   Consideration needs to be given to condensation, unless you operate 'light cooling' where the water temperature is kept above the dew point.  if you do this then you can probably get away with cooling only in some rooms and emitters not suitable for cooling in others.

You will pick up lots of detail tips by browsing this forum.  The forum editor, has also published a couple of books which endeavour to demystify the technology and alert readers to the best practice and potential pitfalls. They might be a good investment.

Feel free to ask lots of questions, none is 'too stupid'.  I have been on here for over two years now, my heat pump was installed two weeks ago (delays due to problems with planning permission etc).  Despite my physics/engineering background, which obviously helps with understanding, I'm extremely thankful for everything I have learned which certainly has made my eventual installation much less stressful than it otherwise would have been (and hopefully better - the evidence to date is promising).

If you have a very open plan house you might want to consider an air to air heat pump (otherwise known as air conditioning).  They are not common in the UK in domestic buildings, although strangely extremely common in a commercial setting.  Other countries, of which italy may be one, use them more frequently in a domestic setting that does the UK.

Hope that helps.

We have a Clivet monobloc- only 3 months in but so far so good with the unit itself and definitely no complaints regarding the noise.

@jamespa Thanks for your insightful reply. And congratulations on the installation of your heat pump. It's a long time waiting! I've been caught in indecision for about 10 months now... I've been researching it thoroughly and have had about a dozen quotes so far. Funny thing is, the installers often tell me different things that contradict what the other installers tell me so I keep getting more quotes to try to find an average of who is actually right. That being said, I don't fully trust any of them for this reason so I'm learning as much as I can.

Good point about the TRVs. I've just looked this up and the solution I think I'll do is turn the manual valves controlling the water flow on the radiators to 1/4.

That's too bad to hear smart thermostats messing up performance big time. I'd like to have some control over my zoning, but what I was thinking of doing was installing two separate heat pumps, one for each floor, which I think can be run without a smart thermostat since they're independent. 

About oversizing heat pumps, I'm going with a heat pump with inverter technology so from what I've heard I should be fine if oversizing 20-30%, which I probably won't be.

@benson Good to hear!