The location is excellent, with public transport (tram) within a few steps. Charles' Bridge is about a 20 minute-walk away. The apartment itself is impeccable, beautifully furnished, clean and comfortable, with all the necessary amenities. The mattress was exceptionally good.
Be aware of the fact however, that there is no free parking on the street and the public parking lots can only be used 6 consequent hours (paid between 6am to 6pm). There is a parking lot in a hotel 10 walking minutes away for 15€ a day, which can be a bitter shock if you don't know this in advance.
Apart from this, I can warmly recommend the apartment. The hosts are rather swift in answering your requests and, in case of problems, they are quite solution oriented.