Great location, clean and comfortable apartment, easy access by metro or on foot from the train station. Nearby a lot of the tourist attractions and metro station.
The main negative point was the bathroom: it was too small and the water in the shower was not even nearly hot enough. Luckily we stayed there during the summer (30 or plus degrees), otherwise we wouldn’t be able to shower.
The drain was clogged and it overflowed every time.
The remote control of the tv was missing.
Also, it was a HUGE inconvenience to walk up to the check in place to retrieve the keys. It was a 20 minute walk from the apartment (and remember that at this point we were carrying all of our luggage around).
They charge 6€/hour to keep your baggage in a locker. This looks bad considering most hostels, even the really cheap ones, will keep it for you for free. Might be good for you guys to reconsider that.