We stayed at Katarina's for six weeks. Katarina and the office staff are communicative, responding in less than 24 hours to all outreach. The office staff gave us a warm welcome and helpful information for Berlin. The location is central and safe. In general, the building is very quiet (when a group staying next to us didn't respectful of quiet hours, the office addressed the issue as soon as we contacted them). The apartment has the basics and a good kitchen set up for a long stay. You will definitely enjoy — the big windows and sunlight that stream in, the ease of adjusting the temperature in the apartment (and warmth during the winter months) and, last but not least, the hot, full pressure shower. The apartment is in short walking distance to everything you could possibly need (including several train and bus options) during your stay.