I was in Prague for a wekend, catching up with some friends.
The Merkur provided excellent value for money - I had a spacious, clean and comfortable ensuite room. I didn't take breakfast. However, the cafe and bar were available to all customers (and the public) was breakfast was over. The reception staff were very helpful.
The hotel is centrally located - the Old Town Square is only a short walk away.
I wouold definitely stay in the Merkur again, if and when I return to Prague.