This place is very central. You can hear the traffic a bit, but after 11 p.m. there isn't that much traffic anymore, so it didn't really bother us. We had our own room which was very nice. I also really liked the balcony. Furthermore, everything was clean. As there are 5 more rooms you may not get into the bathrooms whenever you want to, but we never waited longer than 10 minutes.
Moreover, the apartment is very near two shopping centres and the Balhao Metro station which takes you practically everywhere in Porto!
In total, we had really good days in this flat and a very pleasant stay in Porto!