We spent very nice week in the apartment. The host (Miguel) is very responsive and friendly (even though we met him in person only for a few minutes on the last day of our stay). The self check-in is very easy and works perfect. Also we have received many useful tips from Miguel before arriving.
The location of the apartment is superb, very close to some of the main attractions of Porto, train and metro stations and many good restaurants. The apartment is cozy but has everything needed. It is a little dark because of close surrounding buildings. It is an old building so it is colder inside (which is nice when its hot outside, could be an issue for some in colder periods). Since it is in the city center, it might get quite noisy (constructions, traffic and honking and drank people in the morning sometimes:D).
Overall, it's a great place to stay while visiting Porto, you could walk or just use public transport to get quickly around the city.