Isabelle and her family are such wonderful people. I'd highly recommend staying with them. It's a great location. There are many restaurants, bakeries, and markets, and a nice park near their home. It's close to bus stops and the Metro. I recommend taking the bus to the Louvre, EIffel Tower, etc instead of taking the Metro so that you can see the beauty of Paris.
The only complaint that can be made is that their apartment is across from a hospital. If you want to sleep with the window open, bring earplugs so that you don't hear the outside noise. I'm a very light sleeper, but slept very well with earplugs.