Pros:
The location of the apartment is good, because it lies between the old town and the train station (great if you want to explore also the surroundings of Napoli). If you only plan to stay within the city, I'd rather recommend to book an apartment around the Via Toledo.
The apartment's rather safe (two thick doors with safety locks, almost impossible to get through the window).
Massimiliano seems to be a nice guy.

Downsides:
Unfortunately the apartment is pretty worn down. There is mold everywhere, the mattress is too small for the bed (don't fall in the gap between the mattress and the bedframe!), surfaces are sticky, drains are not working, and a lot of the socket outlets are practically unuseable.

Bottom line:
If you are planning to stay only for two nights, the apartment is ok. But if you are staying for more nights (like us), I can't fully recommend the apartment.