I very much enjoyed my stay at Manon's apartment. It was clean, well equipped and had a nice view of Sacré-Cœur from the terrace. As a young solo female traveller I thought it was a very secure and comfortable property and would definitely propose it for other women who are visiting Paris on their own.
The only things to note are that the apartment is located on the 6th floor of the building (there is not elevator) and that the shower is built inside one of the slopped walls of the inverted dormer terrace (which meant at 5' 9'' I could not fully stand up in the shower). Personally neither of those things were an issue for me and did not at all take away from my experience, however if you have heavy suitcases, are very tall or have accessibility needs this may be of concern for you.
Overall, a lovely place with a very kind and responsive host. The location is excellent: it is a 1-2 minute walk from the metro line 4, very convenient to get to from the Gare du Nord and right beside the Moulin Rouge if you are interested in seeing it.
I highly recommend Manon's apartment! :)