I really really recommend staying at this apartment. The location is fantastic- walking distance from everything in Lisbon (apart from Belem). There are steps and an elevator on the street to the apartment, for those who don't like climbing steep hills, and the apartment isn't too high on the hill itself. For those who don't want to walk too much or climb too many hills in general, the apartment is only a few minutes walking to the tram, metro and trains stations. The apartment is centrally located, but the street itself is relatively quiet, and also feels very safe (we were 3 women, and had no problems walking around late at night). There is a large supermarket and restaurants at a close walk.
The apartment itself is beautiful and very convenient. It's larger and more spacious than it appears in the photos. We were 3, and fitted very comfortably. The apartment was super clean when we received it. It also had everything we needed, including kitchen utensils and spices for cooking. You can tell the host put a lot of thought into making it as comfortable as possible- the windows block noise from the outside very well, there are blinders so you won't have too much sunlight in the morning, the bathroom is equipped with a towel heater and so on.
Vitor is a very gracious host. Before we had arrived, he replaced all the beddings in the apartment to anti-allergenic ones, as one of us was allergic to feathers. He came to pick us up from the airport, and drove us all around the area of the apartment to point out different landmarks, including where all the different stations were and recommended restaurants and supermarkets. He was very helpful all through our trip, quickly answering any question we had over the phone or SMS. We had a little accident with one of the blinders in the apartment, and he quickly arrived to fix it, and didn't make us feel bad about it. He is a fantastic host!
To conclude- if you are looking for a great, clean apartment in a central but not too noisy area, with a great and helpful host, this is definitely the apartment to book in Lisbon.