Magnus' apartment is really great and I can recommend it to any Prague traveller without consideration.
It is situated in a beautiful historical building and really spacious. Perfect for a group of four but could accommodate two more if necessary.
It's really close to Wenzels Square (maybe 5mins walk) and Charles Bridge (10mins if you don't dally, 15 if you do).
The beds are comfy and we all slept very well. Please keep in mind that it might not be dead silent at night since the apartment is so central. We didn't bother and didn't feel disturbed.
The kitchen is equipped with everything you need. There is a Billa and a Tesco around the corner so we made breakfast at the apartment every day.
You could make dinner as well but I would recommend eating out since prices in Prague are really reasonable and the food is awesome, especially if you love meat. You should check out Kantyna, Pivovarský Dům (there's a great small batch brewery connected to the restaurant) and Triton. Last one is a bit more on the pricey side, though.
Parking is a bit tricky. You should consider booking a parking spot at one of the Mr. Parkit garages. There are three or four within 10min walking distance. We used Spálená and Olivova, both were really narrow (at least for a VW Tiguan), and you need to make a reservation in advance.
Magnus and Zolboo were really helpful, Magnus did send us a copy of a booklet that he had prepared to help us getting around in the apartment and the city.