We had a lovely stay at Diane’s apartment, which is in fact very close to the Sacre Cœur and street cafes of Montmartre. The Eiffel Tower and Louvre will require a taxi/Uber/train or will take up the better portion of your day to walk to/from and enjoy (to be expected with how large Paris is).
We found the photos to be very accurate to the space itself, object for object. But as though it didn’t properly depict the roominess or lack thereof. As two average height and healthy adults, we didn’t necessarily find the space too small for us. But I would encourage heavier individuals or groups of 4 to reconsider. The toilet/shower are tight, the stairs to the bedroom are shallow, and the bed is partially wedged under the stairs. We did not find issue with storing luggage but could’ve seen concern for a group of 4.
I found the reviews of noisiness outside the apartment to be inaccurate. You are on a first floor with open windows. But the windows open into a private/closed off courtyard that only tenants in the building may enter. At no point did I feel unsafe or like I was being watched. The courtyard is not necessarily meant to be used either so there was never a group of people sitting and talking outside our windows.
Overall we very much enjoyed our stay in the heart of Montmartre and felt Diane was an exceptional host. Very prompt and gave great recommendations!