Our 5-day stay at Matteo's apartment went great. The apartment is really spacious and clean and well furnished with all the useful amenities as described. The AC specially helped us survive through the Italian summer. It was a 8-10 minute walking distance from the nearest Metro station where one can take all kinds of trains for within and outside of Napoli.
The Piazza Sanita neighborhood is quite chaotic since it is right at the heart of Napoli, but walking around it lets you experience the city like a local.
Matteo is a great host. He is always available online for questions and recommendations for restaurants and things to do. :)