The flat is quite small but for two people is definitely enough. What it's worth of it it's the perfect location, close to two metro stations the will drive you everywhere in the city. Means of transport in Berlin work very well so it is nice being located close to them. Moreover kantstrasse is so full of nice asian restaurants and there is a close street full of very nice shops.
The apartment is ok and Ekaterina is a very nice, punctual, and kind host.