Location, light, and airflow - these are the things I really loved about Cristina's flat. You walk out the door, and you're staring at the S Bahn station. There's food literally within steps of you, and plenty of options within a few minutes walking. Tons of great bars and nightlife in the area, too.
The top-floor apartment has lots of natural light everywhere, and so many windows that you can have a constant breeze rolling through the whole place. It's great! The noise from Hackeschermarkt isn't nearly as bad as you'd expect, and I honestly didn't hear a thing with the bedroom door even partially shut at night. Don't worry about the noise - it's really not an issue.
The place was sparkling clean, a little spartan, but also very home-like - not the sort of generically Ikea-furnished places you find on Airbnb in much of Europe. It's a lot nicer and more inviting, and that makes a big difference in the overall feel of a place. The views from the balcony also cannot be beat.
I'd stay again in a heartbeat, whether for business or a personal vacation.