This flat is very well located to get to many of the sites we wanted to see. It's walking distance to a major train station (São Bento) and to many restaurants and sites. The flat was very clean and comfortable. It's on the 1st floor (2nd floor in US-speak), but there's a cool, old-timey elevator in the building which was helpful in getting our luggage up.
My only complaint (and this isn't the fault of the host) is that there is major building construction on the adjacent building right outside the bedroom and living room windows. Construction started exactly at 8:00 am each morning and they don't hold back. We tried to think of it as a positive in that it got us to get up and start our morning (there's a lot to see, eat, and drink in Porto!), so wasn't a problem for us. But if you're looking to sleep in or if you have young children, this might be a consideration. This is obviously a temporary thing, but from the looks of the construction, I'm thinking it's going to be going on for a while.
Overall great stay for us and would recommend as long as the construction noise isn't a concern.