That was only available on the 3900/2960/300B models which used a linux OS, these models are old models, although still available in places.
It was a weird one, Draytek interface you see now has been on all their models since the beginning of time, but they had these three different ones for some reason, never really understood why.
The best bit about them was they didnt need the constant reboots on some simple config changes, plus some obvious different config options, one of which you say about.
