Our stay in Prague at Johannes' apartment was very nice. One good thing was our communication with Johannes. On our trip we missed one of our connecting flights, so we had to take a flight several hours later, which also ended up being delayed. Altogether I believe we were about 5 or 6 hours later than expected arriving at the apartment. The whole time we were able to be in touch with Johannes, who was able to rebook our taxi and was still waiting for us when we arrived with a smile. As others have noted, the subway and tram are right next to the building, as well as a small supermarket. The apartment itself was very clean and comfortable. There is a lovely rooftop terrace as well, from which you can see into the town center.
I would definitely recommend staying at Johannes' apartment.