I travelled with 2 friends of mine and we arrived at the apartment at 8pm, where Maria was waiting for us. She gave us a city map and some good tips (main attractions and where to eat something typical) to visit it.
The apartment was clean, comfortable and really close to the nightlife district and Trinidade metro stop (you can easily reach it from the airport with Metro E).
The apartment was also eqquiped with towels, bad sheets, hair-drier and a stove. There are also a pharmacy and a supermarket just 2 minutes by walk from the apartment.
My friends and I stayed there for 4 nights and I must say that we could visit all the city center by walk.
I definitely recommend it if you are planning to go to Porto!