I stayed at Caroline's place for 2,5 months, from January to March. It's the perfect central but off-the-grid spot. The metro lines 4 and 12 are both very close and take you through the whole city. All necessary shops are around the corner.
The interior of the apartment is really charming and exactly like in the pictures. It's bigger than I expected. If you're staying for more than a week, you might get annoyed by the bathroom situation. It's small and the everything's wet after taking a shower. Also, if it's really cold in Paris, it can get quite chilly. These are very minor annoyances, the apartment is really worth it!