My parents stayed for 2 weeks at Henrich's apartment. The apartment is as described, very well located in Neukölln, fully equipped, quiet and in general clean (although there were few spots missing). Check-in and Check-Out were unproblematic. One night accidentally we forgot the key inside the flat, for an extra charge someone came to help us out immediately.
As we stayed for a long period, it would have been a nice gesture to get extra towels and bed linens without having to pay extra.