Knoppix style is a single user system with full auto system configuration with each boot.
Beginner is a multi-user system with full (or at least partial) auto system configuration with each boot.
Debian is a multi user system with system setup at initial install but not auto system detection & configuration at each boot.

Debian is the 'recommended' HD install because it is closest to a standaard Debian system. The other two use Knoppix custom startup & there have been problems upgrading to the latest software issues following install. In general it is recommended that the Debian 'upgrade' & 'dist-upgrade' commands not be used, these upgrade all applications to the latest editions all at once but also reset some of the startup procedures to Debian default which has caused some problems.
Personally I have run a Knoppix style HD install for some time without any problems.