This is an excellent location for a Parisian trip with a family. It comfortably fit two adults and two older teenagers. The location was excellent; we were a short walk away from the metro, and two significant Parisien Churches (St. Sulpice and St. Germain de Pres). If you wanted you could also easily walk to Notre Dame and everything around there (although we took the Metro).
The building was a 17 century building, which was quite cool. Everything inside worked and worked well. We never had issues with any of the appliances; in particular the washing machine was reliable which was important for a week long holiday where only packed carry on's.
The hostess was lovely. There some very nice touches when we arrived, she was always responsive to our requests and was very easy going.
The only downside is that it is on the fourth floor of a very old building. That means that there is significant stair climbing on some stairs that occasionally wind. We were all reasonably fit, so that was not a problem, but this is definitely not an apartment for someone with any mobility issues.
If I came to Paris again, and this flat was available, I would come again without hesitation.