Jan is a wonderful host that goes out of his way to make you feel comfortable and provide tips. The apartment is very nicely decorated, modern, comfortable and sparkling clean. Location is perfect for anyone who wants to walk to the main Old Town area. The elevator in the building was crucial for us as I was traveling with my mom who cannot do stairs.
We were there at the beginning of the summer when it's hot in Prague. As you've read in other reviews, the apartment is located in a busy street (as expected being so close to Old Town) so the double windows help in muting the noise. There is a ventilator/humidifier that makes sleeping at night a bit more comfortable while closing the windows, but we didn't want to feel the air directly on us while sleeping, so we turned the ventilator opposite to where we slept. It would be ideal if there was a ductless air conditioning unit as it can get hot at night if you want to close windows to mute the noise from outside at night (and not have the ventilator blowing directly at you).
We would come back and stay at Jan's again!