Location, location, location! First, to reiterate other reviewers, yes the single room is small, but with the toilet and shower separate, those areas aren't too cramped. Also, don't expect normal hotel amenities i.e. daily cleaning & towel change, toiletries, etc. Other than that, this is a wonderful place to stay! You cannot beat its location around the corner from the Old Square -- it is also really easy to get to from the subway station. In addition to the Old Square, there are several restaurants and bars nearby for eating options (including a bakery next store that's perfect for breakfast). I will say it was a little noisy since I slept with the window open, but nothing unbearable.
I had no problem coordinating my arrival with Martin -- he wasn't available but his friend was waiting for me. And Martin invited me to his concert on my last night there so that was an added perk.
Would definitely stay here again when visiting Prague!