This place is in a fantastic location for a short visit to Paris. We are a family of 5 with 3 small children and found many of the attractions in central Paris (including the Seine river cruises, the Louvre, Notre Dame, Les Jardin de Luxembourg, The Pompidou Centre. etc) within walking distance. The neighbourhood has many great bakeries, cafes, patios, restaurants and pedestrian areas to explore within 5 minutes of the flat. Eric is a fantastic host, very kind and quick to respond to any queries.
The apartment itself was very clean and appears exactly as the pictures show. It was a bit difficult to find because it is on a one-way alley with a small front door leading to a passageway between buildings. The apartment is off the side of this passageway separate from any other residential locations (i.e. it is not in a tower with other apartments).
The only thing you should know is that the apartment has a bit of a closed-in feeling due to having one small window in the kitchen looking onto a very small outdoor passageway between buildings and two larger frosted windows looking onto a small alleyway. I would not call it "airy" and there are really no views. The spiral staircase is fine, but it might be a worry if you have toddlers or anyone in your party with difficulty climbing stairs - there is an open hole in the floor to accommodate the spiral stairway. Two of the beds and one of the bathrooms are down in this basement area which has no windows or natural light. Because of the setup of the apartment, there are no walls separating the larger bed from the kitchen, living room and spiral staircase down to the basement, so this may be an issue for parents wanting separation from the children's sleeping area.
Having said all of that, the price for this apartment, which was a little lower than other similarly located apartments, was reflective of these shortcomings. The location of this place is ideal. If you are just looking for a very clean, comfortable, well appointed place to rest your head after long days of walking around Paris, then this is your place. If, however, you are looking for a more glamorous spot with views of the city, the tower, the river or some open, airy space to hang out in (with some separation from your kids in the other room), then I would keep looking.