An hint for all users of this and other similar USB-SCSI adapters: if you experience a system freeze while the OS9 finder is loading, 99% there is a conflict with Toast CD reader extension.
If the Toast component is loaded AFTER the USB-SCSI driver then it will hang the machine. A quick and effective fix is simply to rename the Adaptec extension adding a space before the first letter, so "Toast CD Reader" become " Toast CD Reader", in this way the extension will be loaded BEFORE the USB-SCSI one and the Mac will be happy, no more crash :)