We had a 2 week stay that was good, but had a few issues.
Pros: This is a really nice light, airy apartment in a great part of Porto. The street it is on is just a little off the beaten path, very accessible to great restaurants, and an easy walk to the touristier parts of town. The check in/check out process was great (they kindly let us leave our bags for a few hours until our flat was ready), and answered a few questions during our stay. The balcony is also really great-- the view, the furniture, it's a nice place to sit for an evening.
Cons: There was a bad mildew smell in the bathroom that wouldn't go away. We informed them about it a few days into our stay-- they said they would send someone over and never did. Also, the furniture, while pretty, isn't really comfortable. The sofa is clearly meant to be more of a bed than a nice place to relax for an evening. And speaking frankly, the TV might as well not be there; it's so small and awkwardly positioned we ended up using my laptop for entertainment the whole time.