Me and my wife lived and worked (remotely) out of Costanza's flat for a bit over 2 weeks in March/April.
Costanza was an excellent host - she met us in person, helped us with our luggage, was quick to reply and quickly sorted out a minor cutlery issue we had.
We found the flat spacious for two people. For work we had two separate rooms (one room had a nice, large desk and the saloon had a big table), which was great! The internet is also very fast (1000Mbit, fibre optic). My laptop had no issues connecting to the internet from any of the room except the bedroom (which was no problem for us). The bed was comfortable and there was enough room for our clothes.
There were 5 days where someone in the building hosted parties/loud music till 2am, but for the rest of our stay it was quiet and we had no trouble sleeping.
The bathroom is small and I did hit my head on the beam a few times. The kitchen is compact and had all the necessary items. Contrary to the description there is no oven (only the oven function in the microwave). We had no problem preparing food during our stay.
I'm sorry to say that cleanliness was lacking in places. The floors,linens,towels,bathroom were clean. The kitchen furniture was greasy on the outside and there was some dirt on the inside, the plates were dirty/dusty and the chopping board had a layer of crusted-on food remains. Some pots had been clearly burnt by previous guests and unuseable. We ran everything we needed through the dishwasher before using (the cutting board became clean only after 3 runs!) so it wasn't a major problem, but it was certainly not pleasant.