My partner and I stayed at Felicitas's apartment for 5 nights. The apartment was very clean and had everything we needed for our stay, even a few beers were chilling in the fridge when we arrived, which was a great touch as we sat on the balcony soaking up the Berlin sun (a rare sight for us in Scotland) on our arrival.
There's so much to do in Berlin, therefore we spent very little time in the apartment itself, but when we were there we felt very safe as there is a security gate to the property, and the location itself is surprisingly very quiet, despite being very close to a main road. One of the best things about this location is its transport links, there is an underground station 6 minutes round the corner, and bus stops within 3 minutes walking distance, and these run very regularly, which was extremely handy when we had to be in certain places at specific times.
The check in was very easy, we picked up the key from a key deposit location, and on the way back we had a slight problem depositing the key back, however Felicitas, not only on this occasion, but throughout the trip, was exceptionally quick in responding to our messages, for which we were extremely greatful for.
Overall, we would highly rate this apartment, and will definitely be checking to see if it is available when we come back to Berlin for a bit longer in the near future!