This is great.
I know Berlin quite well as I have lived there for several years.
So: anyone interested in 'real' Berlin, east-Berlin, has to look nowhere else.
Weissensee is one of the last areas where you can breathe an authentic Ost-Berlinische air: very few, almost no tourist, not yet heavily gentrified; a silent and sweet street full of trees; a smooth, quiet atmosphere; very well-connected to the centre and close to a beautiful lake.
The flat is ideal, not only because it is clean and very well-kept, but because you see it is a 'real' flat, not a standardized, fictitious and anonymous one as it often happens.
For me, this is where I want to stay anytime I go back to Berlin.