We (2 adults, 2 children) stayed in Helenes awsome apartment for six nights in july. The location is great (if you like Montmartre, especially), the apartment fantastic and the roof terrace offers a fantastic panoramic view of the north east of Paris + Sacre Coeur on the top of Montmartre.
We were given good directions to find the apartment and had nothing to complain about while we were in Paris. If we decide to visit the city again, I would certainly check if Helenes place is available!