Had a good 3-night stay for our first time in Berlin at Paul & Jana's place. Easy to find via a cab and Jana's instructions to get into the apartment were spot on. The apartment had clearly been cleaned before our arrival and was spotless with great wi-fi and controlled heating. The one issue we had was with noise control; it's a semi-basement studio and when the neighbor(s) above us walked or turned the water on it's quite noisy. Unfortunately for us the neighbor was up throughout the night all 3 days making it difficult to sleep but YMMV.
Overall...a great place to stay especially if you have a bike. For us (walkers) it did take a long time to get to the more central locations like Checkpoint Charlie or Kreuzberg (+30min walking) but there are train stations 15 min walking in each direction.