The software of both devices work in a similar way: when the USB-device is inserted, it registers as three devices: an emulated CDROM containing the program that asks for your password or fingerprint, a 'public' hard disk which is accessable without entering your credentials and a 'private' one which needs the password or fingerprint to be unlocked. The size of these partitions can be adjusted if needed; that operation does re-format both, though.
The encryption on both drives doesn't seem to be compatible with an OS like Linux: the iUSB shows up as a CDROM (with unusable Windows .exes on it) and a 2-partition hard disk. The first one is the private one and it seems to be quite secured: reading from or writing to it gives errors. The second partition, the public one, is accessable, though. The BIO-250U shows up as an (again, unusable) CDROM and 2 separate HDs. The first is the public partition and is usable, the second one is the private partition. Again, it is hidden from sight: this time the enclosure gives a 'no media'-error when trying to access it.
First of all, I decided to open up both HDs and see what's inside. While getting the iUSB open was a bit tricky, I eventually got out the 2.5" HD from both enclosures. Connecting them to a PC using a USB2IDE-converter revealed nothing: first of all, there didn't seem to be a partition table on the hard disks. Secondly, the data on it wasn't readable, a 'strings /dev/sda' (a Linux-command which filters out any readable text on the HD) revealed nothing of interest.
The iUSB-enclosure contained quite a small piece of PCB, considering the amount of parts on it. The large chips, from left to right: a CY7C68013 microcontroller containing support for an USB-2.0-interface, a flash controller and 32MB of NAND-flash containing the contents of the emulated CDROM-drive. The small thing next to the microcontroller is an EEPROM containing the program the microcontroller runs.
The BIO-250U has a PCB that is quite a bit larger, but contains less parts. Completely on the left is the fingerprint-sensor. In the middle is a CY7C68013, the same microcontroller as in the iUSB-device, accompanied by an EEPROM containing its firmware. There's no NAND-flash or flash-controller: the contents of the emulated CDROM are stored on the HD when installing a new HD using a setup-program on the driver-CD.
One thing can be gleaned from the disassembly of the two HDs: the CY7C68013 used in both enclosures is a simple 8-bit microcontroller, without special encryption capabilities. It is too slow to do software-encryption, so if there's any strong encryption, it has to be done on the PC itself.