The flat is very well located, indeed, and everything worked fine in it. The water temp and pressure were fine, though the wifi was a little weak/slow in the midafternoon and early evening, presumably because everybody else was trying to use it.
The room is small but you can see that in the photos and most of our time was spent outside, anyway.
Porto is a fun place for a few days, Mario was very accommodating, too. Our flight with Ryanair didn't arrive until nearly midnight. Mario waited for us to give us the keys and show us around which was very kind of him. The only thing I would have liked is: a bit more advance contact from him. It was only two or three days before we left that he confirmed he would be able to meet us and gave us his phone number in case of emergency.
Other than that I would have no hesitation in staying there again, as a couple, and recommending it to others.