We had a great stay in N&A's apartment in June. It is clean, spacious, well equipped (it had everything we needed) and in a good location (it's not right in the centre of Trastervere but I think that's a good thing). The apartment is close to many good restaurants in Trastervere and is within walking distance to most of the main attractions that we wanted to see in Centro. Public transport is close by for the tourist attractions that are further away. It is a good place to stay to experience a neighbourhood which isn't packed with hotels.
Communication with Niky&Alfre was excellent. We arrived slightly early and Niky came earlier to let us in. She also helped to arrange a taxi on our departure.
We were looking for a quality apartment in a nice suburb which gave us the chance to stay in Rome but away from the tourist heavy areas. The experience met our expectations and we would recommend the apartment to other people looking for accommodation in Rome.
The only thing we would note (and it is very minor) is that the shower might be a little cramped for someone over 6 feet / 182 cm. We found it fine, but taller people will need to watch their elbows.