Great location only one street back from the river and just a few minutes walk to all the waterfront restaurants and cafes. Literally a 1-minute walk to the amazing Sao Francisco Church (nicknamed the "Golden Church") which you should definitely go see.
Cristina was easily contactable and very lovely. She introduced us to Porto with a couple of small bottles of Port in our room and also gave us a thorough run-through of where to go and what to do upon check-in which was very much appreciated.
Like many older cities throughout Europe, the road below is made of stone bricks so you can hear the cars driving through the nearby streets at night so if you'r a light sleeper just be aware of this. You can also easily hear the people walking around upstairs quite vividly, so again, light sleepers beware.
However, these did not hinder our experience as the apartment is great. Plenty of amenities such as toaster, microwave, fridge, kettle etc are provided and the bathroom was a great size and very clean.
We loved every moment of our stay in Porto and can easily recommend Cristina's apartment.