We had a great time in Kay's charming flat! It is easily accessible from Gare du Nord, close to Sacre Coeur and in the middle of a lively, heterogenous area.
The appartment was full of beautiful sunlight, at least when there was sun. It was also clean and well kept. We were there with 4 people, and had no problem at all - the couch is very comfy, in fact, and you have some privacy thanks to having two separate rooms.
And lastly, Kay is a really good host! Fixing a time to arrive was no problem, and thanks to her description, we found the appartment in no time. There were tips and a maps provided, and she even added some more great places to visit while talking to her.
Highly recommended!