We (husband and I) stayed at Celine's place for during our Paris vacation in early September of 2021. The studio is in the busy and bustling Bastille area, but once entered through the green doors it gets quiet, which we really liked. Detailed information was provided for check-in. Check out was easy. Communication was quick and simply. For example, when we arrived we were missing blanket, and when I messaged Celine she promptly addressed it and provided what we needed. Overall it was a good experience. Below is a list of pros and cons below that might help others.
Pros: Quiet for good sleep, comfortable full-size bed, fresh linens, kitchen stocked with sufficient utensils, good number of dishes and silverware, hangers and empty drawers for storage, safe neighborhood, close to public transportation, restaurants and shopping nearby
Cons: No air conditioning or fan (it got pretty hot few days when we were there), lack of ventilation (there are windows but read next point), insects (flies and spiders) may enter through studio window or bathroom ventilation window if you keep them open, small bathroom and shower, vibration noise from the subway (it's not loud but can get annoying).