SSF supports SOCKS v4, v4a and v5 (only main SOCKS features that were implemented in SSH). All these versions are necessary for supporting as many web browsers as possible. Old browsers using SOCKS v4 would need to use UDP forwarding for DNS resolving (to avoid leaking DNS request locally). As you mentioned, there is a "how to" section on the website: https://securesocketfunneling.github.io/ssf/#how-to-browse-p...

For a simple comparison between SSH and SSF performances, you can take a look at the website (https://securesocketfunneling.github.io/ssf/#performances)

Thanks for digging into the code