The flat is nice and well situated. We took the metro a lot (it's a 5 minute walk from the apartment) and walked as well. There are a lot of stores and restaurants next to the flat, it was great. He gave us a map when we first got there; we had no data (and we had a hard time finding free wifi), so that is what we used to get around the city.
Daniele is right next door. We had a problem on our last day and he came to help us, which was nice.
The kitchen isn't that well equipped, so the only meal we had at home was breakfast (but restaurants really aren't that expensive!). We were only there for 4 days so it was okay, but I would have liked the kitchen to have more stuff if I had stayed there for a longer period of time.
FYI, the shower is really (really) small. Let's just say my elbows met the walls a couple of time! But it does the job, so that's what's important.
Overall, the flat is great! It can easily accomodate five people.
If I had to go back to Naples with friends, I would definitely rent Daniele's place again!