We had a very pleasant stay and we can recommend the apartment to everyone. The only downside is that it is somewhat out of the city center. Not a problem to us, but if you hate walking this could be a downside.
The apartment is easy to reach from the airport. Just get of at Lapa station and walk for about 5 minutes. There is a supermarket nearby and some restaurants and café's. On our last day we discovered the Mercado near Boavista square, a great place for a bite to eat or a beer.
The apartment itself is greatly decorated. It has a smart floor plan and it provides for every need. The small balcony makes it possible to take a zip of wine in the sunshine away from the other tourists.
To go short: Great place to stay in Porto. The communication is smooth and fast and the welcoming was more than you can ask for. Not unimportant the apartment was very clean!