I had a great stay at Jan and Martin's apartment. Despite booking at very short notice, they were very accommodating, especially letting me leave my luggage in the apartment on the final day of my stay. Jan was away during my stay but Martin was really friendly and welcoming and always responded very quickly to all my messages.
The room in the apartment is big, bright and spacious. The apartment itself is a good size, modern and well-heated. It is an easy 20 minute walk to the old town, which makes it a great base for your holiday in Prague - I highly recommend staying here!