I loved my stay at Marek's house. It was very clean and cozy. The location was perfect for me, there's trains and buses within a five minute walk, as is a small shopping area with lots of restaurants and a couple grocery stores. If you are ambitious like me, you can walk to almost any of the major sites in less than an hour, but if not, like I said the train is close.
Marek also provides a guide to you before arrival that outlines everything you need to know about the apartment, and suggestions for things to do around Prague!
The only downside is the key is in a different location from the house. Marek said in the guide he can make alternate arrangements to get the key to you, but I was arriving late so I didn't want to bother him. I'm sure Prague is safe but I was a bit nervous a solo female traveler walking down a dark street by myself with all of my belongings and suddenly a man stumbled out a bar. I felt very nervous, especially with all my things. I suggest if you arrive late, to get a taxi or uber to get you to the keys and then home!