We enjoyed our stay at Maria's apartment.
We found it fairly easily using our car's GPS and free street parking was available out the front after business hours. (But beware the one-way streets around Porto - can be quite a labyrinth for visitors!) Paid street parking is also readily available.
Maria welcomed us at the apartment on time. She is very friendly and gave useful suggestions about places to eat, markets and sights.
The apartment is large and includes everything you need for a short or even longer stay. Certainly enough for a couple staying just 2 nights.
It is located in a "artistic" part of Porto, about 15 mins walk to the edge of the centre. Some of the streets along the way are quite rundown, but we did not feel unsafe. It's all part of Porto's often rustic atmosphere.
It's about 45 mins walk to the main tourist areas on the riverfront and longer to the port houses in Vila Nova de Gaia - and a few very steep hills along the way! We drove to dinner on the riverfront, where we easily found cheap parking (€1.2 for 2 hours).