Perhaps the best airbnb we've ever been in, with regards to the flat. However, we do suggest caution in terms of the area.
The flat is absolutely marvelous - top floor of a historic building (1400's). It has a huge terrace with barbecue, tables, chairs etc. and magnificent views. The flat itself is very atmospheric, with old wood beams, beautiful paintings and furniture and candles dotted around the place. There are great extras like a good kitchen and a jacuzzi. The air conditioning is excellent, the bed is very comfortable and the flat is thoroughly clean.
Francesco and his parents (who live in the beautiful flat below) are wonderful and very helpful. We found a bottle of champagne waiting for us, our bed was made daily, our towels changed regularly, and our hosts were so kind as to hold our suitcases all day after check-out so we could roam around Naples a bit more before our flight. It feels more like being in a premium hotel suite than being in an airbnb!
The one (significant) downside of the flat is the area. Quite close to the centre of town but not actually within it. The area is a bit rough and very close to dangerous areas closer to the train station (quite good as a starting point for day trips but downside is the roughness of the area). In six days we experienced a pickpocketing attempt, a mugging attempt and various unpleasant experiences on the streets. This is stressful though manageable during the day and makes it necessary to take a cab in the evenings. The price of the flat is low enough that even with taxis every evening it was well worth it for the lovely flat, but do be prepared to deal with some stress getting to and from sites.