I had a really wonderful experience here. Pénélope was very accommodating- our flight got in at 7AM on our first morning, and she very kindly let us drop off our luggage when her previous guests left (around 11AM) which was perfect. She also gave us tips and suggestions for restaurants, attractions, and navigation which was very appreciated.
The location was perfect- it wasn't a touristy area which gave us 1.) good ambiance (and quiet at night!) and 2.) more reasonable prices for everything from the local bakeries to the groceries. It was a little more difficult than we'd expected because of the wide-reaching (and still on-going) transit strike, but our proximity to Gare de Lyon really saved us. It really is a great location and I can't recommend it enough.
As for the apartment itself, it's small but the size is very reasonable for Paris. I'm not sure if it could comfortably house 4 people, but there were just 2 of us and it was very comfortable. I loved all of the little touches which made our trip easier, from the information she left us to the presence of a washing machine (even though I didn't end up using it, it's great peace of mind).
All in all, I highly recommend.