The #1 reason to stay at this apartment is the host, Joao. He went above and beyond to make us feel welcome and provided us with all kinds of helpful information about Porto. He came to meet us at the cathedral to show us the way to the apartment, helped us with our bags, and took the time to show us a map of Porto and talk us through the major sights plus practical things like the nearest grocery store, and graciously accommodated our late-night arrival. He gave us a bottle of port, and had stocked the kitchen with milk, juice, tea, and espresso pods, plus salt, pepper, and olive oil.
On the other hand, I was a little disappointed by the apartment itself because the photos make it look nicer and more newly renovated than it really is. In real life, the finishes look more tired, and it seems a bit overdue for a deep clean. The basics of cleaning had been done--bathroom was clean, floors were swept, linens were fresh--but the photos make it look spotless and it is not: the walls had dirty handprints and scuffs; windows and mirrors were smudged, etc. I wouldn't complain about this if the photos of the apartment were more accurate, but the photos set my expectations too high.
The bed in the master bedroom looks cool but creaks loudly every time you move and has a very hard mattress (more like a Japanese-style futon than an American mattress, even a "firm" one), which was challenging to get used to. On the flip side, some reviewers mention that mosquitoes were a problem--we didn't have that problem as long as we were careful to keep the lights off when the windows were open after dark.
A note for any solo women travelers reading this: Joao reassured us that the area was very safe, but if I had been traveling by myself I would not have felt that comfortable. The neighborhood felt eerie to me late at night, as the apartment is accessed via a long, winding staircase (with several blind corners) that was usually deserted after dark, and there are a good number of abandoned buildings in the area.
The view from the apartment is wonderful, and Joao is a great host, so I would still recommend it as a place to stay, in spite of the caveats above.