Aposentus is a really great host with plenty of options around Porto.
If you book this apartment, please be aware that it is basically only one room. We travelled with friends and our little toddler. So it was really hard to get some "private space", since all the rooms are basically connected. Plus: There are really loud and annoying seagulls on the rooftop. They kept us awake at night - or woke us up in the morning.
However: The Aposentus team were really helpful and forthcoming. The location of the apartment is superb and overall we really recommend the place - if you are aware of these facts.