We enjoyed our stay in Susana's flat. It is on the first floor of a small block of flats above shops in an ordinary, very non-touristy street, and faces onto a quiet area to the rear of the flat. It was quiet at night apart from the ubiquitous seagulls (which I don't think you can escape from in Porto!). It's a 5-minute walk from the nearest metro line, which leads straight into the heart of the city and to many of the popular touristy areas.
The flat is small and simple but perfectly ok, and has a good balcony (enclosed but with big windows you can open) which is handy for drying things or just leaning out of. The kitchen has all the basics that you might need for preparing a meal. The bed was comfy, and you can close the shutters completely for darkness or leave them slightly open to allow cool air to come in at night. The bathroom is fine except that the shower setup is tricky to use without flooding the floor, though we mastered it with tin foil and a bit of practice (and the water pressure/temperature are good).
Susana was friendly and welcoming, and was there to greet us when we arrived even though our flight was a bit late. She gave us an excellent tip as we were hungry and needing somewhere to eat: the restaurant just across the street, Estrela da Lima, is very good. We ate there several times! We found it to be much better quality than other restaurants serving similar type/price of dishes.
Thank you Susana!