We had a wonderful stay. The flat is ideally located which is the most important in my view, especially if one stays only for 3 days. It is 3 min away from metro(the yellow line which gives access to the main parts of the city quickly) and to velib stations, if one is hungry, not necessary to walk kilometers, everything is Le Marais, and very nice shops in the area.
The flat is even nicer than on the pictures and very bright. The kitchen is well equipped and the bathroom is cute. We had absolutely no problem of noise during the night (and I am very sensitive to that!).
The stone floor of the stairs are, yes, a bit damaged, as you can read in the other comments. But if one is a bit careful, this is really no big deal.
If you don't know where to stay, go for this flat!