What a wonderful place to stay!!
The centre of Napoli is very busy of course, and quite touristy. However, this flat is in a very quiet and charming area called Bagnoli. However, it still has very good links into the city. There are a couple of train lines. The Metro line 2 is only a few mins from the apartment, and the train only takes about 20 mins to get into the centre. It's very convenient really. Also Bagnoli is right by the sea, it is a truly wonderful setting.
Furthermore, Diego and Carmela are wonderful hosts. Incredibly friendly people, who will be more than happy to support you with whatever you need. When I return to Napoli, I look forward to staying here again!
Finally, the apartment itself is also very nice. Very large room, with a nice balcony overlooking the street, and with a view of Lady Nisida Island. Plenty of space too with a combined living room and kitchen. A really lovely apartment to relax in after a long day out for example.