We had a perfect stay at Grunewaldstrasse!
It is a very spacious, bright place with a kitchen that provides you with everything you need and a bathroom you'd wish to have at home:) There's a coffee&backery downstairs and two supermakets next door.
The U-bahn station is very close by - but it does take you a while to get to the city center (26 Minutes to Hackescher Markt, 17 Minutes to Stadtmitte/Brandenburger Tor).
Elena was super friendly and very uncomplicated.
We enjoyed our stay a lot and would certainly recommend the place to anyone that doesn't want to stay in a newly renovated, spacious apartment with a wonderfully friendly host.