We really enjoyed our stay at Maria's apartment. The apartment was clean and sufficient for our quick, 2-day visit. Looking at the photos we expected the place to be a bit bigger, but it wasn't a major problem since it was only 2 of us and we were out most of the time. However, I can see how this might be a tight fit for 4 people.
The location was awesome as most of the old town is within walking distance. The check-in process went very smoothly as well, and we really appreciated the local tips.
All-in-all, a pleasant stay. I would definitely recommend this place for a quick trip to Porto.