For a city trip, the apartment was rather well suited, as it is located near a metro station and there are plenty of supermarkets and shops around.
There is no air conditioning, so in the summer heat, it might get really hot in there. (ventilators were provided, however).
The biggest flaw is really the bathroom with its mouldy corners.
The hosts were nice, albeit being a little late for check-in, and gave us maps as well as tips for what to do in Porto.