I just bought the adapter thinking it would speed up transfers from a Lexar FW800 card reader to my 2011 MacBookAir. Unfortunately it is slower than using my existing Lexar USB2 card reader!
A quick test with a 16GB Lexar 300X CF card with 2.8GB (133 CR2 files) of images:
FW800 = 80 seconds
USB2 = 95 seconds
Still it does give me a separate backup "system" in case something goes wrong with the USB side of things...