We stayed at Patricia's flat with 4 people; two adults, two children. The apartment was perfect for us: enough space, very nicely decorated (it actually is just the way it looks on the pictures), clean and well equipped. Patricia is welcoming, easy to reach and flexible (we could leave our luggage after check out, to pick it up when we left for the train). The apartment is just a 12 minute walk from Gare du Nord and 5 min from the nearest metro station. I would recommend this apartment to families like ours or 4 very close friends. Not necessarily to two couples: one of the bedrooms is only accessible through the other one.
All in all we couldn't have wished for a better place to stay, certainly for this price. If we return to Paris, we will surely stay at this flat.