We stayed at Katharina's place for 2 nights in June. The location is about a 6 minute walk from the east train station which has tram, bus, U-Bahn, S-Bahn, and regional train stops. Very convenient for travelers who do not have a car. Get an MVV day pass for single or group because you really need to take the train, bus, or tram to get to the touristy areas of the city. The space is fairly good size for a studio in a large city. There was room to spread out our bags and still walk around the apartment. Entrance was very easy, there's an exterior door to the street to get into the small entryway and then a code to get into the ground floor unit.
There's generally no AC anywhere in Germany which we expected but it happened to be very hot during the time we were there. A small fan would be a nice touch to circulate the air because even with open windows all night it never got below 80 F in the apartment. The only other con I can think of would be for those travelers who want to cook meals. It is a very, very small kitchenette with a hot plate instead of a stovetop. Certainly doable but it would be really crammed trying to cook for yourself there. Wasn't an issue for us because we ate out every time.
Overall we enjoyed our stay and had no issues. Would recommend to solo or couple travelers.