Using a tripod in Prague is no problem as long as you don't interfere with traffic (either people or cars). I used my Flexaret there and had a few older people approaching me to chat about the camera as they used the same all those years ago. They were so pleased to see a young guy use a camera like that in this digital age.
Be sure to pay a visit to Skoda Photo, they are located in the street called Vodickova, it's a street that connects with Václavské Námtestí square. It's a big photo store with a nice part of old camera's (which you can buy) and a good range of film (also rollfilm). The Staff speaks a little English but not much. These are the guys who hooked me up on Foma Film, got a roll for free when I bought a Flexaret III there, I was lost on Foma after that.