We had a very pleasant stay in Mario's studio which was, albeit small, very cozy and well-situated (everything is within walking distance !). Another good surprise : the room is very well insulated sound-wise, so not too much rowdiness at night !
Mario was very helpful upon arrival, providing us with a map and recommendations, as well as when we left - we could leave our luggages in his care and print our boarding passes with his printer.
Overall the perfect Porto spot for a short-term stay.