Exactly, it only replaces the Ten no Koe Bank, not the Ten no Koe 2.
Ten no Koe 2, Backup Booster, Backup Unit and any CD-ROM device all works in the same way for Backup RAM, and you still need one of these to save to. The unofficial TED OS is only used to copy the save data in the 2kB Backup RAM to the SD card or vice versa. It doesn't simulate the Backup RAM or anything like that, if that's what you think.
I believe the unofficial OS only works with TED v2 though.