Seagate FreeAgent Go Pro for Mac 500 GB external drive,
which supports both FW800 and FW400 and USB2.0,
when plugged in via USB2 shows up as:
Unknown USB bridge [0x0bc2:0x2200 (0x000)]
works fine with '-d sat', '-d sat,12', '-d sat,16'.
(over firewire it appears to only work with -d sat,12 -T permissive,
but that is a separate issue)