Maria's apartment was great for our family of four. We only stayed for one night in March 2022, we were on our way back from spending a week on the Amalfi Coast and had an early flight out of Napoli.
Like the other reviews mentioned, the apartment building is very old, and the entry courtyard from the street seems like you might be in the wrong place, but once you walk up the 3 flights of old stairs, the apartment itself is large, modern, and very comfortable. Good sized beds, large updated kitchen and bathrooms, nice furnishings. It was also quiet.
Easy ~20 minute walk to the Quartieri Spagnoli for dinner, and only 15 minutes to the airport in a taxi.
I will also add that Nina and her husband where very helpful in checking in. We ended up arriving 1.5 hours earlier than we had planned, and they clearly came to meet us from another engagement.
I would definitely stay here again for Napoli sightseeing, and highly recommend Nina and her husband as hosts.