My husband and I stayed in this apartment for a month, and it was the perfect home base. The apartment is newly renovated, modern, and clean (completely up to our high standards living in a high-end apartment downtown in America). You have all the amenities you could ask for — whether for a short-term or long-term stay (from a TV with a full range of channels and Netflix capabilities, to a washing machine). My favorite part was honestly the 2 skylights in the bedroom and 3rd one in the upstairs bathroom: they made it so nice and bright. The building itself is also great, including an elevator to take you up to the 3rd floor (which isn't very common in Europe).
The location is very convenient: easy walk to all the historical parts of Porto, right next to both bridges to walk over to the Gaia side, on a wide enough street to make it easy for taxis/Ubers to reach, and on a quiet street where you won't hear any noise at night. If you want to be right outside all the bars and going-out areas, it MAY be a bit of a walk for you, but we preferred to be somewhere we could easily sleep all month.
The communication is managed by a management company, so they're very prompt at responding via the app (although I could never reach them by phone). They were also nice enough to answer all sorts of weird questions I had, like where in Portugal one would buy specific home goods, for example.
One small tip for future travelers: they only had an all-in-one shampoo and body wash when we stayed there (so you may want to bring your own shampoo and conditioner ladies).