I stayed a whole month at Marion's place and I loved it.
Pros
+Marion is just a great host, quick on replies and always welcoming.
+The apartment is just as you see in the photos, very cosy in a new condition with all the basic needs. Very well designed.
+Building is lovely, quiet, no problems at all.
+Montmartre is one of the loveliest place in Paris with great food and easy metro connection to anywhere in town.
Cons
-WiFi is a bit weak and at times unreliable
Really a great place to stay and I'll be very happy to visit Marion's apartment again. Heart fully recommended.