Basic but comfortable accommodations in a vibrant neighborhood. Easy access to busses (the 38 bus South was my go-to option) and metro trains (used the 2 train a lot). Walking is an option (Mont Martre 25-30 mins away) but may be a bit much for most (Notre Dame about 45 mins South).
Plenty of eating and drinking options right out the front door (great little patisserie right across the street, nice brasserie a couple doors north, all you can eat sushi a couple blocks south, kebab shops all over, etc).
The room I stayed in was very basic (bed, bedside lamp/light, small table and stool, two electrical outlets, small closet) but the bed was big and comfy and there were French doors to a small-but-nice (north facing) balcony.
Three bedrooms share a split bathroom (shower and sink in one room, toilet/WC in another (tiny) room). Had no issues as I and the other guests seemed to be on different schedules.
Shared entryway with hot water pot, teas, microwave, maps/brochures...and that's about it.
Two elevators (5th floor apartment).
I was there to sightsee and be a tourist, so all I really needed/wanted was a place to sleep and use the bathroom. For that it was great.
I never actually met Sebastien (or his mom) but his communications were quick and helpful.
Had one issue when another guest took the shared key for the front door, but that was quickly resolved (and for a small fee I was able to get my own front door key for the rest of my stay).
All in all I was very happy with my stay. Saw tons of things, ate lots of good food, and was very happy with the value/"bang-for-the-buck".
I would absolutely stay there again in the future.