I stayed at Isabelle's place with my gf: Dec. 26 -Jan2, 2022.
we liked:
location, coziness, quietness, flexible check-in, very responsive, very friendly, comfortable bed, central location: near many coffee shops, 2 min walk to St. Germain de-pres metro, 10 min drive to many must-see places, friendly welcome - bottle of wine and 2 glasses! (I am sorry, we broke on glass!), very spacious apartment: good when you have lots of luggage. The heating was really good, & big windows facing the street.
we did not like (very minor):
there was food kept in the refrigerator, that did not bother us since we did not use it, but it gave the feeling that somebody lives there (which is ok).
note: the stairs (up to the fourth floor) should not be an issue for young people, so it was not an issue for us.
but maybe this is an issue for older people.
other notes: there is a piano there so if you play the piano that's good for you, there is a fireplace but the instructions say not to use it.