We stayed for a few days in Mara's flat.
It was perfectly cleaned, well-equipped and nicer than on the pictures! It is located in the historical city center (but no noise once you enter) making it easy to visit the town by foot. It's also very simple to reach from the airport with the nearby metro.
Due to the pandemic context, we didn't meet Mara but she left us clear instructions and was very quick to answer our questions. She was also kind enough to let us stay a few more hours on check-out day as our plane was later in the evening.
I would definitely recommend this place if you are planning to stop by Porto !