10/10, exceeded expectations. :) I honestly have no gotchas / nuances to warn about. Everything was great. I was hesitant because of the small number of reviews, but everything was awesome:
Apartment is exactly as seen in the photos (only brighter, and with a backyard full of plants! There are shades on the windows, so you get to enjoy sun when you want it, and close things off for the night), super clean, QUIET, and feels very new, with various amenities and small touches (everything from a microwave, full kitchen furniture set with oven - to hairdryer, electric heater if you need it, and extra blankets).
A very warm welcome and help from André - thanks again :) really great hospitality.
What else to add - everything is as per description, a great and (again) very clean apartment with all you need, location you can see yourself - very central - perfect for exploring Porto; it's quiet at night (which was important to me, I was working in the mornings etc.); has a large table (with good wifi) for doing work and having dinner; etc.
Lots of great cafes and bars around if you want that (for example Early is great for breakfast right across the street, there's Apuro vegan bar around the corner, etc.), good public transport connections.
Would definitely recommend. Hope to come back some time. Thanks again :)