Absolutely fantastic duplex apartment in a very central location.
It is on the top floor of the building and inside is very spacious.
I stayed with my girlfriend (so didn't use the smaller bedroom), but the whole apartment is great.
The kitchen is on the second floor of the duplex and opens out onto a private balcony which faces west so you not only get to see the Clérigos Tower in the distance, but the sun setting behind it in the evening.
The apartment had all the amenities we needed for our stay.
Martha (the host) was unavailable for the time we were there, but she left us in the very capable hands of Ricardo.
He came to meet us for check-in and was prompt and very welcoming (and very fast to reply by message).
He gave us a huge list of recommendations for arts and culture activities, as well as good places to eat and things to try.
The apartment is a couple of streets over from some really good bars and no more than 10-15 minutes walk from most of the main attractions in Porto centre.
As it's so central, it may be worth bringing some ear plugs if you are a light sleeper :P
It was quite warm whilst we were there so we often had the windows open, which obviously let some more sound in.
Overall, we had a really great stay and would highly recommend it based on the location and value for money :)