Martin was a great host! We were caught up in the Berlin Airport strike and had to cancel one of our days at last minute, even though not Martin's fault he refunded that lost day. That alone makes Martin a top host for that action even though his cancelation policy conditions didn't require him to refund the lost day.
The apartment was clean and beds were comfortable. This sort of apartment really makes you feel at home, more so compared to hotels. We had also spent a few days at a similar priced hotel, so had a good comparison. The other members of our group would prefered to have stayed here rather than the hotel, unfortunately it was booked out.
As for the location, it is very near to the center of Berlin. Many places to shop and eat nearby. The train station is 5 mins walk. There is a shopping center with food store called the Arkaden less than 5 mins walk for your food supplies.
Conclusion: We will definitely stay here again should we come back to Berlin.