The flat is very well located and close to the main sights and there are supermarkets just some meters away. The communication with Mario was excellent and as there are no elevators and the flat is in the 4th floor it was great that we were helped with carrying the suitcases upstairs. One thing to mention is that you need to leave the water running for quite a while until it gets warm.
We had an amazing time in Porto and the flat was a good place to stay and very quite even though it was very central!