The flat is located very well. We have been in Naples for 5 days and could easily reach most important places by foot. The host is very nice and considerate. She even sent us information about the city before we arrived so that we were well prepared!
All in all, I think this is the best thing you can get if you are on a tight budget. The only noticeable downside would be that the ceiling in the upper rooms are quite low but that really isn't that much of a problem if you get used to it. All together, we had a great stay!