The apartment is very spacious and has an excellent central location and also a great feeling of security and ease. The one we stayed in overlooks the Holocaust memorial (not sure if Heinz has more than one). Was impressed with the size of the living room and one bedroom especially but all were big enough to put down a yoga mat if you wanted and it would be a great apartment to keep bikes in (Berlin is a terrific location for biking with many dedicated bike lanes.) because you could easily wheel it in through front door, onto elevator and right off into apartment. Kitchen was fine except a little frustrated that the tiny refrigerator did not have a freezer compartment (looked like there had been one that fell out). When we asked about this to the agency that rents for Heinz they just said some of their refrigerators have them and some don't. Also don't anticipate a microwave - there's a very nice coffeemaker and good selection of pots, pans, dishes and cooking utensils. Again I don't know whether Heinz has more than one apartment in this complex. Check in was very smooth - we called ahead when we realized we'd arrive slightly after 6pm and they gave us the combination to a box for picking up the keys - very easy once we found it!
We also had great WiFi reception the whole time and wanted to mention that because some other reviews had complained about it (maybe a little less good in the farthest away bedrooms). Also when we had a little trouble with the support for the shower in the bathroom (fell down) they sent workmen up right away to fix it after a brief phone call. It is also a very historic area - we had a car the first night and they assigned us a parking place for 10 euros that turned out to be located right above Hitler's bunker (covered over by a parking lot rather than memorialized.)