Everything related to the Stefano house was perfect. The place is close to the public transport, railway and buses, and pretty close to the airport (about 45 minutes). Also, the apartament is situated in the beautiful Vatican area, you need just to walk a few minutes. In the nearby street, you have a food store and some wonderful restaurants. Stefano was a real friend for us, because he helped us with a lot of things (from how to get the proper train to get to his house...to the very useful recommandations).
So, everybody, if you are not decided about booking his home, do it now! I will, next time when in Rome, for sure!