I stayed at Apostolos' flat for a few days during a conference trip to Berlin. It's a lovely place in a lovely area of Berlin. Easy to get to from both the city and outskirts of Berlin with two U5 stations nearby and prob. 3-4 other U/S/tram lines in a 10 mins radius.
The apartment itself is great, too - very clean, a good size and with some quirky pieces of artwork and decoration. Pretty much all the basics you'd need are there (if you didn't bring your own), there's a Späti next door and 2 Rewe markets just 5 mins walk away. Wifi worked well for my plethora of devices, too.

Check-in and -out were smooth and easy - my arrival time in Berlin was super-nicely accommodated! I really enjoyed my stay - would def. come back for my next Berlin trip if Apostolos' apartment is available again.