Leo's place if a very decent alternative than staying in a hostel, it will cost you the same as the cheapest hostels in Napoli (ones without kitchens and which can be very dirty) if travelling with two people. You have the added, and much appreciated security and privacy staying in his studio apartment.
Leo was very accommodating towards us as we only decided last minute to stay in his flat at 7pm that night, he offered to pick us up from the train station but we had already started to walking towards the flat and met him there. It is extremely central only 6mins walk from the main train station, Napoli Centrale and 2mins to the famous 'da michele' pizzeria.
We found everything we needed for our short visit in his house, we were there only for 1 short night so we can't comment on how it would suit staying for longer.
Only issue is, and was mentioned to us by him, is that the power can trip when the old switchboard overloads with heavy use from the building. This happened to us a couple of times but was very easy to rectify by flipping it back near the front door.
If you are on a budget visiting Napoli and are considering staying in a Hostel, this is the place for you. 5* for value and great hosting.