My girlfriend and I stayed in Jans apartment over New Years and it was fantastic!
We used the instructions he gave us to walk from the train station to the apartment where we met and the apartment shown to us.
The apartment is great. It's pretty spacious and was in the best location, within walking distance of the best parts of the city like Charles bridge and is surrounded by great places to eat and drink. It really is in the old town square.
Jan has a guide to Prague which is fantastic too. It's full of the best attractions to check out, and awesome suggestions on where to eat and go for a drink. We tried out a few of the restaurants/bars listed in the guide and loved them.
This was the best air bnb apartment we stayed in during our holiday.