Stayed one night with my girlfriend in low season. The price was very affordable, yet breakfast was included. The hostel is located a 5 minute walk from the nearest Metro station (which has access to all three lines), and a 15 minute walk from the Old city. The hostel in itself is almost undetectable from the outside, but very cosy once you get in. Free internet and computers for use were available in the common room. Staff was very friendly and provided us with help for anything from car parking to places of interest!
As it was very cold in Porto during our stay, the old house's insulation did not keep up with the small radiator in our room. Thus, nights were very cold. Also, private rooms with adjoining bathrooms were not available.
All in all though,it was a very nice hostel and I'd happily stay there again!