Very easy communication and check-in/out. Never used the Key4friends app before but it was sooo easy and made our life much easier (due to a flight delay we arrived @4:00am and had no issues entering the apartment). Location is close to all historical sites (with 20-50min walk you can reach everything). Apartment is protected from traffic noise. We picked this apartment due to the high ranking of cleanliness, which I would say was ok but further improvement can still happen.
Communication with Tatiana was very quick and easy and she was helpful whenever we needed.