Plusses: Spacious (especially for Paris); excellent location; quiet; nice building and courtyard; comfortable beds; attentive, proactive host; easy check-in and check-out.
Minuses: Very little privacy; tall people are sure to bump their heads on beams upstairs (which shed dust); anyone with mobility issues will have trouble (rooms are upstairs, bathroom is downstairs, with no handrail on the stairs... so, if you need to use the bathroom in the middle of the night, you'd better be fully awake); cleanliness was maybe 7 out of 10; there's a light in the adjacent entryway that flashes randomly into the apartment and will keep you up at night (curtains aren't very thick).
Having said that, we were there for 9 nights and got used to the apartment... and actually enjoyed the stay. Thank you!