The apartment is great - VERY clean and well eqipped. We had a perfect stay, we will recommend the apartment to friends and book it again when going back to Porto.
You can walk to the center or take the metro, so the apartment is perfectly located. It is quiet, only in the morning you hear cars passing because of the cobbled streets that you find everywhere in Porto.
What we also liked a lot is that when we had a question, you got an immediate answer.