The flat is very conveniently located, in the Testaccio quarter just to the south of the Aventine hill and in walking distance to several famous sights like the Circus Maximus and the Bocca della veritá, most other sights can be reached directly by bus, as a lot of bus lines run by in the immediate vicinity. Also the Ostiense railway station is in walking distance.
Despite the comparatively central location, it is very quiet as the windows face the courtyard. The flat itself is very clean and well-furnished. We stayed there as a familiy of five.
Vera, the hostess, offers reasonably priced transport from the airport which was really convenient and saved us a lot of hassle. Also the check-in worked very well.
The Trastevere quarter, famous for good eating, is just on the other side of the river. However, my recommendation for real Roman cooking is to stay on this side of the river, as the Testaccio boasts plenty of good restaurants without the throngs of tourists and the obnoxious waiters trying to lure you in their respective eatery.
There is a binder in the flat that contains plenty of information.
We can absolutely recommend this flat.