I stayed in the Studio near Kastanienalle for 5 weeks and absolutely recommend it. I felt at home from day one. The apartment is beautifully decorated with modern design furniture (just like you can see in the photos). It is fully equipped with a small fridge, oven, electric kettle, toaster (no microwave), wifi, cable TV, etc. The place is super clean and the bed is large and comfortable. The bathroom includes a washing machine (very convenient for long stays). The only thing to keep in mind if you have mobility problems is that it's located on the third floor and there's no elevator in the building (like in most buildings in Berlin). It is also very quiet, one can't here anything when the windows are shut.
It's located in the neighborhood of Prenzlauer Berg, which is very hip and has plenty of restaurants, shops and cafes. The apartment is just 5 minutes away from the U-Bahn stations of Rosenthaler Platz (U8) and Senefelderplatz (U2) and 3 minutes from trams M1 and 12.