Simone was a charming host responded readily when I reached out. The apartment, as many reviews note, is indeed in a very quiet alleyway in the heart of Food Central Trastevere. You do need to be ready to walk to historical sites, as public transit takes about the same time as your feet (Trastevere is a bit of a transit dead zone - but this also allows for characteristically narrow streets and night life.
Regarding the accomodations: The first thing I noticed was that this space is not designed for short people. I (162 cm) could not reach most things in cabinets or on shelves, and if I could, I couldn't see what I was reaching for. So if you're my height or shorter (and cook), be prepared to move things around if you visit, appropriate the chair in the bathroom as a footstool, and to move everything back when you leave. However, as the kitchen is very, very small, somewhat sparse, and has virtually no work surface, it doesn't really invite the preparation of any elaborate meals. Otherwise, perfectly functional.
The shower is pretty good and the water pressure is decent - but be aware that the water circulation system/pump will make a drilling noise after you use the facilities, so, as in all older buildings, your apartment will not always be silent. There was no laundry drying rack and the dining room table could not be enlarged as a workspace when I was there, but this and a few other minor issues might potentially change when you visit...The noted lack of air conditioning (as stated in the listing) was not an issue for me, but if you're here in the summer, DO get a plug-in mosquito repellent or two. The bed is on the harder side, but I slept well and found it good for my back.
Overall, the location is great and the space is small but cute. Just...it IS an airbnb and some things will be worse for wear unless pointed out to your host before your stay.