Charlotte's flat is perfect if you are looking for a cozy place where you will feel at home. I stayed there with a friend for a week and we were more than happy. The size is ideal for two persons and it is very comfortable. It is close to the Metro 4 which takes you to the Gare du Nord and Gare de l'Est in a few minutes, Montmartre is in walking distance and the Metro-connections to the most important sights in Paris are very good. The quarter is very lively with many African shops and market stalls. However, the flat is calm because the windows lead to the backyard.
Charlotte was already abroad when we arrived so that her sister welcomed us and gave us the keys. Communicating with both of them was uncomplicated at all times and they were flexible with the check-in and check-out times so that it fitted in with our train connection. Charlotte gave us loads of recommendations for things to do in Paris and the best bakeries and restaurants nearby. She also left some cheese and wine as a welcome gift - she really makes you feel like staying at a friend's place :) I definitely recommend staying at her place and would consider it again for my next trip to Paris.