The flat was enormous and just like in the pictures. Clean, well located and not at all cold as some reviews claimed.
That said, we were instantly taken aback by the passive-aggressiveness of the rules that were sent to us just before arriving and also more rules hours before check-out. It seemed like anything we did could mean extra charges that they said were up to the cleaning service.
I made a mistake when booking and selected six guests instead of seven. However, the original price of the place was the same no matter the amount of guests, so I guessed that wouldn't be a problem. It was surprising that there were only six of everything -six duvet covers, six pillows, six towels, six cups... Not even a couple extra ones just in case someone needed more! So I contacted the host about it and the answer (which came on the next day after insisting, so far from quick) was that if we wanted another towel we would be charged extra -which is very disappointing considering the price was the same from the start no matter if there were six or seven of us.
Also, for a place where the rules appear to be so strict and any mistake could mean extra cost, several things were broken or wouldn't work - hair dryer, toaster, TV... The Wi-Fi connection was also useless. The beds were huge but not so comfortable and the sofa bed was not a sofa bed, but a really big regular sofa.
So, it is a big, lovely space which could be way more comfortable if the hosts behaved more empathetically and were not just after your money (20€ more for every half hour your check-out is delayed in case there's some problem!). But considering how they not only weren't helpful but also were really slow in answering my messages and did nothing to help us solve the mistake, I just wouldn't recommend this place to anyone.
There are plenty of similar flats in central Berlin and I'm sure there are way better hosts as well.