This place is even better than we expected based on the photos and reviews. To start: location! Very close to subway and all nice areas (Bairro Alto, Chiado, Alfama) within walking distance. However, I liked 'our own' area (Mouraria) in which the apartment is situated the most. It's a maze of photogenic small streets and not so touristy yet. In June, it's the San Antonio festival with street parties everywhere and the one on the square near to the apartment is great.
Second, the apartment is quite spacious (although I don't recommend for more than 2 people) and very clean. Shower's good (but you have to be cautious with hot water so no long showers) and all amenities (shampoo, towels etc) are there. I also really liked that it's double glazed: this makes the apartment very silent at night (area is also quiet, but in June you will have some street parties until 1am or so, but just very little white noise in the apartment). Points for improvement: the beds are two singles, would have liked a double bed. Also matress was quite firm, but that's a matter of taste.
Third, the hosts are very nice and easy to communicate with. We were allowed to leave our luggage after check out time, which was great. Thank you Didier and Silvia.
So: look no further and stay here! You'll love it.