This apartment is in a really fun location with lots of lively stuff going on. Everything is happening literally right outside the front door, so if you like that then this place is perfect for you. If you want some space from the action though, this might not be the right one. Most of the noise doesn't make it into the actual apartment because of the double windows - but on the weekend the sounds of the performers in piazza trilussa will still reverberate through the walls (amateur renditions of pink floyd and the eagles EVERY NIGHT). This is a trendy and crowded area with tons of great restaurants (just wait in the line, it's worth it). I saw lots of american and british tourists here, so I don't feel like it has a super 'local' neighborhood feel, but it is special. It is a 20-30 minute walk from this place to most of the major sites in Rome. The metro doesn't run to Trastevere; there are buses you can catch nearby as well as a street tram, but it seemed like most of the routes did not take you to central areas.
Elena was a really nice host - she was communicative and supportive to us during the whole stay. She allowed us to include an extra guest the first night we stayed, and made sure we had extra towels and linens for them. She met us at the apartment for check in and continued to be responsive whenever we had questions. She contacted the building administration when we reported the wifi was not working. She had new towels brought to us halfway through the stay. She provided local tips and recommendations, made us a reservation at a local restaurant, and booked us a taxi to the airport when we left.
The building housing the apartment is very old and cool, the apartment is a walk up two flights of very European steps (ie be careful when you are drunk). The place is fairly modern and tidy. We didn't need to buy much (just toilet paper, soap etc), as most basic things were provided for us there. As for cleanliness - the linens, surfaces, and most spaces were really good. There was some mold in the shower and the floors could do with being wiped down throughout, but otherwise it was pretty clean. The bed was really uncomfortable, unfortunately; lowest model ikea mattress, 4 inches high, on flat wooden slats. The wifi connection was weak and only worked in the bedroom. Elena reported the problem for us, and the coverage did improve afterwards, but was still not good. There was also no washing machine in the building, which was listed as an amenity, so that was unfortunate for us as we stayed for a whole week and packed light - Elena said she would have this fixed going forward in the posting with airbnb.