As many others have said, this apartment has the magic combination of extremely central and yet very quiet. The minute you step out of the gates you are in the center of Napoli. (Try the fried fish at Decumani 31, twenty steps away.)
The place is simply furnished but has everything one might need---well, except for a washer/dryer, but this is not so common. There are a couple of steps between the bedroom and the bathroom, which may be a risk for people who have to do their business in the middle of the night while half asleep. These minor details aside, this is an excellent place to stay.
Our host was only a virtual presence, but we didn't need much help anyway. We had no trouble getting into the apartment with the instructions provided. She did order us a taxi when we left, and that was extremely helpful because there are no taxi stands nearby.