Very good experience. Check-in on time, and even a bit earlier. Instructions for check-in/out are all very clear, as well as some nice tips about Porto and what to see, when, etc. Also, nice restaurant recommendations.
The apartment is also very clean in a renovated building - everything looked just as on the pictures.
Overall, only positive experience.
I would recommend staying at this place. And when I come to Porto next, I would try to stay at this apartment again.