Great location near Rossio and up a nice restaurant filled street (great coffee place at the end called la Fabrica) The Flat is very clean on the top floor. Paulo is an instantly likeable man and gave us great tips on where to eat and see the city - he was also on hand throughout our stay should be have needed him. We walked everywhere within Lisbon and felt safe at night in his apartment and the area it is in. We ate out each evening but the kitchen was well equipped should you want to cook.
We had some issue with noise from the renovation happening to the building next door, but this is out of the hosts control and we may have been unlucky with the nights we stayed - maybe check with Paulo when it will be finished if you are not planning on being up and out sightseeing each morning.