Guillaume's flat is one of the loveliest places I've stayed in Paris. The view of Sacre Coeur is beautiful. The location is great: Close to the Metro, easy for food shopping etc. Initially the area seemed a bit odd (Blvd de Clichy has a lot of sex shops on it), but it is safe and in fact not as scary as I had imagined. It became quite entertaining to watch the tourists. The flat itself is well-equipped and clean and the space is good for one person or maybe two. I ate in many meals and had everything I needed.
I highly recommend it and would stay again!