Martin’s place is extremely well located for your trip to Prague! It’s right on the main square and walking distance from everything you will be interested in as a traveler there. It also is nicely decorated, and has some very useful amenities (like a full kitchen and a washing machine)!
But one note to future guests: if you are driving to Prague, I would advise you park in a public parking lot instead of the parking spot Martin offers. It is not in the same location as the apartment, it’s a hassle to coordinate with Martin to park there when you check in, and to get your car when you are leaving. Also, you basically don’t have access to your car during your stay (i.e., for day trips, etc). Not sure how expensive public parking is in Prague, but I would have paid more to not deal with those issues.