We stayed at Katja's and Germain's during four days in late august. To make it simple, here are the ups and downs:
Ups:
-The hosts were lovely and they have a beautiful family
-Both of them were helpful in terms of finding our way around or supplying us with missing items.
-The apartment is very lovely, floors, bathroom and linens are clean and is well decorated :)
-The AC was well functioning and very enjoyable, at this time of the year
-Even if there are five people living underneath the apartment (including 3 kids) we never heard them once
-House is very secure (double locks) and stairs and hallways are clean
-Three metro stations are very close to the house

Downs:
-The neighborhood doesn't have much interesting restaurants or bars
-The streets aren't super clean and the area can be a little noisy at night (loud music till midnight during one of our 3 nights)-that was probably just bad luck!
-The metro ride to get to the city is a little long and can sometimes discourage you from going out again at night
-The kitchen space in the apartment is quite tiny, though we did manage to cook three suppers there anyways, but we had to be thorough with our cleaning or else the space becomes easily messy
-Some kitchen tools were missing (can opener, baking pan, spatula)
All in all, if we were to go back to NY/Brooklyn we would most definitely stay there again, probably because of the host's kindness, availability and the very cute apartment we found in East NY which was well worth the price :)
Camille and Felix