The apartment was an interesting space. It is in an "attic" space--meaning that the main living area has a sloping ceiling. You need to sit on cushions or beanbags under this sloping section. We (one adult and three children) stayed for a week, and it was okay, but you would probably not want to stay any longer. The kitchen was very compact. I couldn't figure out how to use the oven properly, and it was difficult (given the space constraints) cooking in it.
It is an upstairs and downstairs apartment. On the lower level is a shower and a large bedroom. On the upper level is the living area, kitchen, a toilet, and a loft bedroom. The best aspect of the apartment is it's location. It is a 2 minute walk to Cardinal Lemoine Metro station; and it there is a lot to see in easy walking distance from the apartment. Check in was very easy by following emailed instructions. All in all, a great stay.