We only stayed in Justine's apartment for one night, but we enjoyed it a lot. It was very clean and cosy, with lots of little nice touches around the place. The big window opens out onto the courtyard which was really nice too.
It's in a good neighbourhood, with quite a good selection of restaurants and bars nearby, without being too loud. The apartment is close to the station and it's very easy to get around the city from there.
If you are in Paris for a couple of nights, I would recommend this nice little place!