We found the apartment to be excellent. All four bedrooms were large, the beds comfortable, linens excellent. The kitchen was well stocked and the apartment was spotless. It can easily accomodate 5 to 8. Having 3 bathrooms was really a plus. The only drawback was that the apartment is on the first floor and there can be street noise at night, particularly Friday night from the bar downstairs. (Most other nights were quieter) If you are a light sleeper consider disposable earplugs, as I used. On the other hand, we loved the bar and stopped there for drinks 3 out of 6 night. Testaccio is a great neighborhood, not touristed, with great dining options and good shopping for food. It is about a mile walk along the Tiber to get to the Capitoline hill, so it's not in the middle of the sights, but public transport is readily accessable, as were cabs.
Our hosts were excellent, arranging transport too and from the airport. Check in was a snap and they were easy to communicate with during our stay. Highly recommended.