This "chambre de bonne", as such micro-apartments are called in Paris, is a real gem: It is highly functional and practical, inspite of the little space, and I highly recommend it.
I spent a month here in March 2022, and had a good time. I would definitely recommend the apartment for one person only, not more. The bed is comfortable, and does sleep two people, but if the second bed is drawn out from beneath the first one, there is literally almost no room at all left to stand up.
The tiny space is used in the best possible way. I had fun thinking of it like the famous Tetris computer game -- you simply need to take fun in handling things carefully and put them in place after you use them, and then move on to the next piece you use or do.
The stove works very well; the water boiler works very well. The internet connection works very well, too.
The bathroom cube is very functional, equipped with a hair dryer. I am 1,60 m and had no problem. Anybody 1,75 m or more might feel really crunched, as the ceiling is quite low. But it's manageable.
The house is quiet; I met some neighbors here and there, all were friendly, and no noises were audible from next door (I heard that this can be a problem in old Paris houses).
The apartment is on the 7th floor; the elevator goes up to 6th floor, and the rest is stairs, but not many (this also is a Paris classic). The view is absolutely stunning: you look out onto the Sacré Coeur while sipping your tea or coffee for breakfast, very memorable.
The quarter is very touristy, but at the same time you reach everywhere in no time from here, and have the Centre Pompidou, Notre Dame and the Marais at the tip of your finger.
The window in the apartment is functional too: If it's open, it's noisy from the street below and the (too many) maraudering youngsters at night; if it's closed except for the airdrift the noise is shut out 80%. If you close even the airdrift (not really recommendable), then you do not hear anything from outside anymore. Hence: a good, isolated window.
The heating is not sufficient to warm the apartment on chilly days, but there is an electric heater which does a good job. However, once it's on, the room is filled with its ventilating noise non-stop. But it does get the room warm in 10 minutes in the morning. March 2022 had some very warm days, and then no heating was required at all -- this probably means that during summer the place will be quite warm (that is my guess).
In short, a great place to stay, and the price is reasonable, compared to other Paris options. The location is unbeatable. And the practicality of the place is very pleasant.