What a lovely place to stay for our family of 5. We were here for the 4th of July week and had a great time. Location is the best. The apartment is literally a 5 minute walk from metro stops, charming restaurants and bakeries, and the Rue de Montorgueil which is such a wonderful avenue filled with all types of restaurants and stores.
If you don't mind a walk, the Louvre is 20 minutes or less, and the 1 Line on the metro from there can take you all the way through the gardens, Concorde, Champs Elysses, and the Arc de Triomphe.
Our kids loved the loft above the stairs and it was their preferred bedroom. The Merveil team was responsive with questions and there were a few that popped up during our week stay. The floors appear to be original wood and some panels aren't as flat as others so I would recommend being careful walking or bringing indoor slippers. The stairs inside are a metal spiral staircase which requires care going up and down. If you are taller than 5'9" you will have to duck a little to get past the 1st/2nd floor threshold which has padding for safety.
We used the washer/dryer and it worked well. Hot water is instant for the showers although the upstairs bathroom is typically European in being tight. 1st floor bathroom has much more space. Beds, linens, towels were all very good. A/C was great and kept things cool in the summer heat. It had one error but that was fixed within 12 hours by their team.
Given what the rates average for this apartment, our week was definitely expensive at more than 4x the average rate. Most likely that was due to our timing as we came during a busy American vacation period. That's the reason for the fact our review isn't 5 stars all the way down. But if it fits in your price range, it's worth it for the local experience.