I stayed for 7 nights at Marcello and Fabiana's apartment and I just can say everything was great. Even though I booked one night before my arrival in Rome, the communication with Marcello was very easy.
The flat is in an authentic, quiet Roman neighbourhood, just between two underground stations of the line C (around 10 minutes on foot). I came by car and could park right in front of the building and took the metro to go to the city every day.
The flat is big enough for two people, with a nice bedroom and a kitchen with a sofa. A washing machine is also in the bathroom.
Marcello and Fabiana live in the next-door apartment and are really nice and welcoming hosts, so if you need something, they'll be there for you.
All in all, I just can recommend you to stay here if you happen to visit Rome!