We had a good stay at Dorota's. The flat is simple and a bit old-style, but functional. It has its own charm and a very nice view. The position is excellent for visiting the city center. Just keep in mind that getting there from some parts of Porto (the docks, Sao Bente station) requires facing some steep climbs.
Dorota is nice and arranging, you won't have to worry if you need an early/late check-in or wish to leave your luggage in a safe place for some hours after the check-out.