We have to start by saying that Caterina was an amazing host. We got to Napoli late in the evening and she was very accommodating for our late arrival. She also helped us with a taxi back to the airport when we left. The house itself had plenty of space for the three of us and is quite beautiful - it's as-described in the pictures and info on the listing. The kitchen was well stocked. The only thing we were missing was either a tea kettle or microwave to make tea.
As for location, Napoli is a very hilly city. There is no getting around that. You are always either going down or up. There is mass transit - and that does help some - but when you visit Napoli, you will walk and climb, a lot.
The house is located about halfway up the hill on a "street" of stairs (down to the water and up to the Vomero). We ultimately decided that we liked this location, both because it is beautiful on the stairs overlooking the bay and because it kind of makes it centrally located. Just know that luggage, groceries, etc. have to go up or down the stairs - even with the funiculare (a cable car that runs up the length of the stairs from Toledo to the Vomero. It runs until 22:00 and costs the same as a trip on the metro).
We really loved our stay and would definitely stay at Caterina's place again next time in Napoli!