I was staying at Yanns with my boyfriend for 2 nights. The location is perfect if you want to experience plenty of fantastic food, coffee, sights without going too far away!
The apartment is clean, conveniently close to Sacred Heart church and the rest of Montmartre without noisy neighbors! it is located at 4 floor, so be ready for calf-exercises ;) few square meters used perfectly for a stay of 1-2 persons. everything is in one room - the bed is elevated, however wasn't a problem to climb in! The kitchen has what you need for non-complicated cooking, we only used it for morning coffee. The bath/toilet separated from the rest by a glass door- so if your not intimate with your traveling partner - you will be after a while ;)
In general- good experience staying at Yanns, who was a discreet host, made everything ready for our arrival and prepared us with very detailed guidance in advance!