We loved our stay at the Casa Azul - it felt like we were living in an IKEA catalog (and isn't that the dream?!). The apartment was super clean and well appointed for 1-2 people. There was a lovely balcony, though we didn't use it because it has been getting chilly and it didn't get much sun (at least in Nov).
The location is on a very quiet street, for which we were grateful, especially at night when the bedroom was super quiet. It is, however, a good 20-30 min walk (or 5 min walk plus 5 min metro) to the heart of downtown Porto. And it's all uphill on the way back to the apartment :) There are good grocery stores and pastry shops nearby.
Antonio and Anabela were excellent at communicating, checking in to see if we had everything we needed, and swiftly providing anything that would make our stay better.
I highly recommend this place!