Good value for the money. Communication is excellent, they are very reactive and helpful. The location is good, not exactly in the city centre, but you can still walk there and there's a metro station with all the main lines 3 minutes away from the apartment. For check-in, you have to pick up the key at their office around 15 min away (walking) or you can pay 10 euros to have someone waiting for you.
The apartment itself is comfortable, the kitchen is super well equipped and it's nice to have a balcony. It's on the last floor so I didn't have any noise issue. You can hear traffic if you leave the windows open, but that didn't bother me. The photos look a bit more modern and bigger than in reality, but it's still good. Only thing I would maybe complain about is the bed, it really is not the most comfortable... But for a couple of days, it's fine :) So all in all, I really do recommend it, as it is a good and affordable option to visit Porto!