The flat is nice and the location is excellent. It's just a few minutes walk from Václavské náměstí but still it's a quiet street. The process of getting into the flat is a bit cumbersome but it's understandable from the perspective that it's a company which runs several flats. That said, in order to register and take the keys, you're supposed to go to their office on Václavské náměstí, which means the check-in hours are not very flexible and this might be a problem if you arrive late in the evening - you will be asked to pay extra to check-in after 20:00.
In the flat there are no slippers, so bring some with you. You will get one just big towel per person. In the bathroom, there are no hooks for towels, no stand or any convenient place for the toilet paper, and no dustbin, hence ladies' hygiene in certain days might be difficult. There is a bidet, which is nice.