The apartment is spacious and should be enough for 1 or 2 persons.
Location is prime right in the middle of action. But this comes at a price: you are near the trains, buses, cars and people walking on the streets. You hear everything. Sometimes I could not sleep because of the noise. Had to close the windows to prevent noise but that resulted in the apartment getting a little stuffy at night when it is hot and humid in Lisbon at night. Tried to work out the fans in the rooms, but they are small and clunky, and unless they are close next to your face then they are useless. I think they should be replaced.
If you are arriving early to check in, you have to wait until 5:30pm for the maids to clean the apartment. The maids were late in my case and came at 6:30pm. Although I was able to check into the apartment at 1:00pm, I had to wait until after 6:30pm for the bathroom to be cleaned and so I could finally get in the shower.
Otherwise the place has Wi-Fi, good furniture, nice small kitchen, and a descent size bathroom. The owner is responsive and helpful with tips.
Bottom line: take this place if location is what you are looking for, but be aware of its cons as I mentioned above. Fans should replaced. The apartment should be cleaned at most at 2:30pm.