The place is very well located, in a typical and charming area of Lisbon, near the castle. It's comfy and functional. Very good welcome from his friend Lucia, and his father Eurico was friendly and helpful, as we didn't meet William.
The downside of this flat is clearly its bad soundproofing: you really hear the sound of the street (people, binmen, etc...) quite loud, and it was really lively during our stay. Light sleepers, don't forget your earplugs !
Except that, very good place to stay in Lisbon!