We had a great experience and we loved both the apartment and the location. It is in front of the main train station, connected with almost every single line and also with the airport. Also it is really close to the touristic center but outside the touristic chaos, which I consider perfect.
We travelled with a 1 year-old baby and it's completely adapted to this case. There is a lift to get to every floor and no stairs at the entrance, plus there was a lot of space inside our room for the kid to wander around.
I'd like to add a special mention to Carolina, who recommended to us the best places to go and was always available and fast for every question we had.
In short, I would totally recommend to choose this flat to have a good experience in Porto :)