Before arriving I was a bit worried about the location of the flat, but it appeared to be just great: the house was easy to reach. It's just two stops away via tram from the centre of East Berlin, Alexanderplatz. Moreover, there's a bus stopping almost in front of the door that can easily take you West to the famous Berlin Zoo, taking stops near 1/3 of all the main Berlin's landmarks like Potsdamer Platz, Tiergarten, Europa shopping centre, Keizer Wilhelm church etc. Tip: first thing to do at the airport is to buy a Berlin Welcome Card that allows you to travel free via Berlin public transport for 24, 48 or 72 hours (and have some discounts for museums as well). The Friedrichshain park in front of the house is a nice place for walks and in late autumn trees look astonishing.
The flat appears to be bigger than it seemed on photo, I think anyone would like the simple, neat and spacious interior with small smart details. The bed is absolutely the best one I've ever slept on in journeys. The room, the kitchen and a little pantry has anything you need to feel yourself like home.
Ann-Katrin is very friendly and hospitable, ask her about nice places to eat, her advises just hit the mark for us.
We're quite choosy travelers but would rate this place 10 out of 10. Really hope to visit the apartment again.