I really enjoyed my stay in Kopenick, which is a beautiful part of Berlin, close to a lovely forest and right on the river. There were good connections from the flat to S-Bahnhof Kopenick (c. 12-15 with the tram), but it is worth being aware that you are about 40 minutes with the S-Bahn from Mitte. The flat is well-situated for three different supermarkets (EDEKA, Penny and Rewe).
I found the flat reasonably comfortable for two months on my own, although there were a couple of things I needed to buy for self-catering in the kitchen and it would have been good to be able clean/mop the floor properly.
Baharbin was responsive to questions and provided good instructions regarding arrival and departure.