Stayed for five nights with a friend. Communication with Catalina in advance was good and precise, and the host Luiz, who lives in the same building, was friendly and helpful throughout the stay. He let us use the room for a few extra hours when our flight home was cancelled, which was much appreciated.
Walking there from Gare du Nord takes about ten minutes, but the metro station Poisonnière is only a minute or so away. The location is great. There are bakeries, restaurants, and grocery stores nearby, and getting around is easy.
The apartment is located on the fourth floor above ground floor. It is very small, but it looks new and modern, and it is clean and functional. There are practical shelves above the sofa bed for storing clothes and the such, but travelling light is recommended. We also recommend eating out. The kitchen has a water cooker, cutlery, plates, and cups (in addition to the microwave and fridge), but there is no chair or table, so when the sofa bed is folded out, there is no place to sit and eat.
Something to note is that there is not much privacy if you are two people, as the shower is the centrepiece of the room and has a big glass door. So you should be comfortable being naked in front of each other. Also, you might want to ask for separate blankets, as there was only one there when we arrived (this was fixed for us the next day).
All in all we had a nice stay. The room was a nice and practical «base camp» for us, and I can recommend it for other active travellers who pack light and eat out.