Overall it was a great place and I would recommend staying here! Flavia's mother checked us in easily as Flavia was in Porto. The place was very clean and modern, with all the amenities we needed--AC, kitchen, washer, etc. Easily the best feature though is the location, since it is right in the middle of everything. We had planned to Uber (or maybe metro) around the city, but we ended up taking literally zero cabs and trains because everything was so walkable, such as city sights, the river, and restaurants. And the view (from common area and patio) is incredible!
One important thing to note before you book is the climbing involved. It is perched on a hill, so walking places will involve ups and downs. And the building does not have an elevator, so you will be taking 3 flights of stairs to the apartment. It is not an issue at all (and totally worth it) if you are mobile, but be aware if you have any young children or mobility-impaired travelers.