The apartment of Cristobal is very well located: less than 10 minutes walk to Saint Peters Square and entrance of Vatican Museums. And 5 min walk to metro station (Ottaviano). There are some bars and minimarkets downstairs where you can buy breakfast.
Cristobal was there to check us in around midnight.
Apartment is nice. The only problem we had was the noise: in august Rome is very hot and we had to leave the windows open at night to cool off the apartment (which is under the roof). Because of that we got quite some noise from the restaurants and traffic for the Square and Street. Earplugs are really necessary.
We did not suffer from the bad smell some other reviews mentioned.