Our overall experience with Alex and his apartment was very positive and we would definitely recommend this apartment to friends traveling to Prague. The location was perfect, just as described. All the main attractions were indeed in walking distance and there are many restaurants around the apartment. Alex met us by the building at the check in time and was very helpful. We really only had two issues with our stay -
1. One of the bedrooms doesn't have a double bed, rather two single beds pulled together with not-so-great spring mattresses.
2. In the shower of the same room, the knob switching between the faucet and the shower head tended to get stuck every once in a while and it was impossible to hang the shower head. Also, I agree that a bathmat could have been useful.

With that said, the apartment was very well equipped and perfect for our needs (two couples traveling together).