I loved staying at Catherine's flat, and while I never met Catherine, she was a informative host. The details in the materials she provides were very helpful, detailed, and accurate, and everything is exactly as described. The beds including fold out sofa were comfortable, check-in and check out was very easy. I didn't hear too much of other neighbors except neighbors to one side having loud conversations a few times and their door is so close it sounds like your own flat door is opening, but such are tight quarters in an old building.
The location is very convenient to two metro lines from which you're only about a half hour from central Paris. And though there isn't a lot going on in the neighborhood, it is nice and quiet. A small warning about getting there: I will say Gare du Nord is big, busy, and confusing; I never managed to find the location to leave luggage (or even the floor it's located on), but once you get out, or get to the metro to take you closer, the instructions are quite clear.