We stayed for 10 days: husband, wife, 20 y.o. daughter. We are healthy, strong, active. Many comments.
1. Location is superb. Lovely neighborhood. 5-10 min walk from Seine. Galleries, cafes, restaurants, historical places. Secure neighborhood & building. Near metro --St Germaine des Pres and Odeon best.
2. Hosts lovely and gracious. Very very helpful. Met us with cold champagne. High recommendation.
3. Lots of hot water, washer works fine, all utilities and wifi work fine. Shower is a bit public--not walled off--visitors should be friendly.
Downsides: (NOTE we were there in middle of horrendous Paris heat wave, T~100F.) Rooms were quite warm. + fan, no A/C. Main bed is too small for average american adults. couch-bed was pretty hard, though daughter is resilient. + some street noise (ubiquitous in Paris.) Toilet is down a flight of narrow spiral stairs and if this is an issue in the middle of the night, be careful. I would recommend this to a strong young couple who plans to spend a lot of time outside exploring especially the left bank. It is safe, comfortable, well-placed, and able to supply adequate comforts when done exploring Paris.