The apartment is absolutely gorgeous. Great value for money. We were 12 people and loved our stay there. The rooms are clean and well equipped. The location is also good, with just two metro-stations to the main railway-station and just a 15 minute walk to the center of Prague. The hosts are very friendly and respond almost immediatly. We had a small problem with the heating on our first day, and they showed up within half an hour and fixed it. The breakfast is also delicious and for 3 € a day also quite cheap.
The only thing i would change is the sound-system in the living room, because it is only connectable with iPhones. We had one fortunately, but groups without iPhones should consider bringing their own speakers. But that's really just nitpicking compared to the rest.
Overall just a great experience with no real downsides. Almost too good, as the comfortable apartment can make you want to stay there and keep you from exploring beautiful Prague.