I recently tested an OWC Mercury Elite-AL Pro mini drive enclosure, which is equipped with 2-FireWire 800 ports, a USB2 port, and an eSATA connector. Without the aid of instruction sheet, I was able to install a standard 2.5 inch drive inside the enclosure in about 15 minutes. I simply removed two screws that held the port cover so the drive assembly could slide out of the case, inserted the hard drive in the slot receptacle (securing it with 4 screws), and reattached the port cover. Powering up the drive is where I ran into minor difficulties which I later solved.
The temporary problem that I encountered had to do with attaching the drive to my Mac using the eSATA cable. As a bus-powered device, the OWC Mercury Elite-AL Pro mini mounts instantly as expected when it is used in conjunction with a USB or FireWire cable. However, the internal drive will not mount if the OWC device is connected with just the eSATA cable.
In order to benefit from eSATA’s faster throughput rate, you have to attach your Mac to the OWC Mercury Elite using both the eSATA and FireWire cables simultaneously. According to OWC, the chipset inside the Mercury Elite automatically chooses the faster eSATA connection when both cables are used at the same time.