Myself and 6 friends stayed in Berlin for a festival, with the intention of just using the apartment as a place to sleep and shower and for that purpose it was fine. The apartment itself was nice enough, if quite basic and small, it was a 2 bedroom apartment but with enough beds crammed into those rooms to sleep 8. It was clean and very close to an u-bahn. The apartment had decent WiFi, but for some reason only 3 of us could connect at a time. The apartment was expensive for how small/basic it was but served as a good base to head out and see Berlin from.
As a host Oliver was punctual, check in was at 3pm and his colleague met us outside the apartment . However, during our stay, a chair leg gave way beneath my friend as he sat down (thankfully he wasn't badly hurt) but Oliver later tried to claim damages for the faulty chair, and didn't respond to my messages when I tried to speak to him about it.
Basically this apartment was quite expensive for what it is, and is less somewhere to stay and more somewhere to just sleep and then go out into the city. Small and basic, but also clean and convenient. Just make sure to be very careful whenever you sit down!