My partner and I stayed at Federico's apartment for a week, and it was wonderful.
Federico & Alessandro were both incredibly responsive and welcoming. They sent a brilliant list of recommendations for everything from restaurants, days out and even Gelateria's.
The apartment is lovely, and is quite spacious. Easily big enough for two people. We found it quite quiet up there, despite what the noise levels were on the street below. One word of warning, the stairs are quite steep and there are 4/5 flights so be careful if that would be a challenge/if you are bringing a lot of luggage.
The location is fantastic. You are pretty much 5 minutes walk away from the "centre" with the Dome, and everything else is walkable in at least 30 minutes from there. You don't need to worry about cabs etc at all. Despite such a central location, we didn't find it was particularly noisy or rowdy. A perfect place to retreat to after a long day sightseeing.
We had a brilliant time, thank you.