Great little apartment to explore Berlin from. Depending on where you want to visit it's a 10-25 min walk to all the key sites, we just walked everywhere and it was the perfect staging point to see the delights of Berlin.
Airport was a 15min walk and 20min trian away and cheap, when arriving (by train) we walked from central station to apartment which took 1hr but we saw loads of sites.
Only real downside for me was the mattress could be better, my back didnt feel good on long active days then sleeping. A better quality matress would have been appreciated, sleep is key when being so active in the day.