The apartment was as described, spacious, homey, quiet. Everything was clean, the kitchen well equipped. Petra awaited us and was friendly. The neighborhood is nice, though not much to do nearby. Access to the nearest U-BAN is very good, a short walk to the station and from there - no problem to get anywhere. All in all it was as expected. A good alternative to a nice stay in Berlin and a good experience.
One problem was that the internet didn't work when we arrived. Petra did what she could to solve the problem, but it turned out that we didn't have connection for the first two days. Luckily for us, it just started working, after we have plugged the devise in and out, on and off, etc....I guess Petra really did her best but hadn't we managed to fix the device, we would have stayed with no internet. I believe this is something that has to be fixed prior to the arrival of the guests.
I do recommend this apartment as a good choice for a stay in Berlin.