We stayed at Mathilde with a group of 9 people (7 adults and 2 children). It was just perfect, the children had a separate place to play expand their Lego constructions, while the adults where chilling with cheese and wine in the common space.
The showers worked good and all kitchen items were good and functioning.
We only got 1 key for the whole group (I must say I did not requested a 2nd one), but this is something to keep in mind if you think you would need to access the apartment split in 2 groups.
The location is fantastic, walking distance from Notre Dame and the Seine. Bakery and supermarket really close too. We had a great time. Thank you, Mathilde!