Me and my girlfriend spend 5 nights in Giovanni's flat and we really enjoyed our stay! Since Giovanni was out of town we had the flat wholly for ourselves. You have to be aware that "climbing" up to the 5th floor can be exhausting and it is definitively worth the effort! You are welcomed by a spacious flat, nice kitchen and amazing balcony. Giovanni allowed us to use all of his stuff including coffee etc. and immediately responeded to all questions. He had nice recommendations for us and although not being in town made sure that we had a good time.
Apart from the stairs you should also be aware that the flat has no AC so that it can get pretty warm in summer months like August. But using Giovanni's fan and opening the windows definitively helps. :)
If you wanna get to know Napoli Giovanni and his flat are a great choice!