I was replacing my MacBook Pro's original HD with an SSD so I bought one of these cases to hold the new drive while I duplicated the current drive to it. I tried three times to do this with the case connected via FireWire cable and each time SuperDuper! failed with less than 5% copied over. I switched the connection to USB and the duplication went fine.
I thought the problem might be an incompatibility between the FireWire controller and the SSD but I having tested with the original internal (spinning platters) HD in the case and found the same problem.
Odd thing is I bought the same case in August 2012, put a terabyte 2.5 inch drive in it and it has since been working fine as a FireWire connected Time Machine external on my mother's Mac. Different firmware/chipset maybe?
With USB 3 enclosures much cheaper it's hard to see a reason to buy this if you can't rely on the FireWire functionality.