My husband and I stayed here for a week with three other friends and it was perfect. Communication and check in/check out were very easy. The location and neighborhood are really wonderful- easily walkable to everything in the Marais and close to multiple Metro lines for easy access to the rest of Paris. The street is lively, but the interior facing bedrooms were quiet.
The building is lovely and very well upkeep, the entrance was well secured and feels very safe- and the host mentioned that everyone in the building was aware that the unit was rented out- which was actually really nice because we didn't feel like we had to lie about being Air Bnb-ers, or sneak around as long as we were quiet and respectful of the residents obviously.
The flat itself is really beautiful- it's huge (for Paris) and lovely- just like the photos. It's relatively well equipped (plenty of linens, pillows, towels, etc) and enough kitchen essentials (pots, pans, tableware, etc) were there for us to cook and eat at home comfortably once we bought some staples and basic supplies (salt+ pepper, napkins, trash bags, dish soap, etc.). Although the owners don't live there often it seems, the flat is lived-in enough (in a good way- as opposed to some bare-bones places rental companies own) to have everything you need to really feel at home (eg: soap dishes, oven mitts + kitchen towels, toothbrush holders, hair dryer, iron, hangers for clothes, portable fans for the occasional warm evening, etc- things real people use in real homes that you only notice if they aren't there). The fold-out couch for the 5th person might not be comfortable for someone to sleep on it for a longer period of time, but it was good for a few nights and it is easy to close off the living room, which was nice.
We'd definitely highly recommend staying here, and it was great for a bit of a bigger group as there are multiple places throughout the living room and kitchen to congregate and hang out and plenty of space to eat together. We loved it and would definitely come back!