Although I am not sure if I met Kate or Alex (this is their rental agency where several people work) everyone we met was very friendly and quite helpful. Although the check-in was mentioned at 3, since we arrived at 7 in the morning they prepared the flat for us by 1 so that we could check-in as soon as possible. More importantly they give you a lot of information about the city and the whole area.
Coming to the flat itself, I was very happy with it! It is exactly as in the pictures and even then I was impressed with how nicely maintained and set up it was. The kitchen was very well equipped and there is ample space for 6 or more people (in case one brings their own sleeping bags say) on the floor! The main city is a a 15-20 minute walk but Wenceslas square was so close and the metro from there took us everywhere (I came with my older parents who were not able to walk so much).