I can't say enough good words about this apartment. First of all, it is truly gigantic by Parisian standards. We've spent time in many places in Paris, and this is by far the most spacious we've ever seen. It is also very comfortable and well-maintained.
The location is also fantastic, at the heart of the 6ème, with great boulangerie, patisserie, neighborhood restaurants, farmer's market, etc. It is really close to Raspail and Montparnasse (with Rodin's Balzac statue to boot), yet on a smaller street so there's no noise. Steps to Line 12, and very convenient to 4 and 6 as well. Also very close to the Jardin du Luxembourg, which is our favorite Parisian spot for kids.
The service was also very good. We wanted a late check-in, because we had tickets for the Louvre on that afternoon, and they were 100% accommodating. Mathieu was very nice and helpful showing the apartment. The place itself was very clean and with great amenities. My only complaint is that the wi-fi was a little spotty, but that's nitpicking...
We highly recommend this apartment, and would definitely stay again. Thanks a lot!