Luka's place was spotless, convenient, well equipped, and very well located for nightlife and transit. I'd definitely stay again.
The only trouble I had was trying to cool the apartment down. The week I stayed was warm for Berlin (25C during the day, 15C overnight), but because the apartment was level with the sidewalk, and there were no window bars, it would have been unsafe to leave the windows fully open while sleeping or away from the apartment. You could leave the windows securely cracked with the ceiling fan on, but the apartment would stay very warm (the building hallways were also very toasty). Any other time of year this wouldn't have been an issue, but the apartment could use some improved ventilation.