I've got a few points regarding Karens place: as other guests already said, this is not a place for 4 people. We were 3 people and for us it was quite small. The whole place is maybe 17-18 m², so i would say 2 people max. could stay here! We also had problems with the wifi. It probably worked for 1h in total during our 4 day stay, so now we understand why some people said there is no wifi available. Maybe they will fix it.
Other than that the place wasn't in the best condition: the wall besides the windows has a few holes and cracks in it and it wasn't as clean as we wished it to be (e.g. there was a razor on the mirror cabinet in the bathroom, some hair was on the floor and in the corners), but for only a weekend stay it was okay.
In addition, there was no second blanket and after requesting it we sadly still didn't receive it, so all 3 of us had to sleep in one bed (I think he just forgot, because he took care of all the other things we asked for! But either way, not the best situation). We were fortunate, that the one blanket and bed were very big, so we fit inside, but it wasn't optimal.
For the positive points: it has a great location! The arc de triomphe is basically right around the corner. Around the apartment are also places to buy food and the metro station is very close.
I also want to add that Karen and the guy who takes care of the place were quite nice and always responded fast to our texts.
If you don't expect much and don't plan to stay a lot at home, this is a fine option for you.