Mattia's place was great with an amazing view. It was lovely to wakeup looking over Naples and Mt. Vesuvius from the bed. Certainly the best view of any place we stayed in our trip to Italy. It was very clean and smelled nice like a hotel. It was cozy but not cramped and exactly what we needed. It was inside several locked doors so it felt very safe.
We had a bit of trouble finding the building initially because Google didn't understand where the address was, but we got there eventually and she showed us everything and was very nice. The location is very close to the train station and a bit on the outskirts of the main tourist part of Naples so we didn't come home to stop a lot in the middle of the day. The area might feel a little sketchy at night although we had and saw no incidents whatsoever.
There is an elevator that requires a 10 cent coin, which was something we had to remember as the apartment is on the 16th floor! She keeps a bowl of 10 cent coins that you can use just in case.