It seems to work, but I have not yet confirmed how fast it is. It seems to be very easy to have it accidentally pop out of my brand new, "HP Pavilion dv6t-2000 CTO Entertainment Notebook PC." It also seems to have "play" sideways and does not seem secure. This is my first ExpressCard 54 device, but I was told that the narrower ExpressCard 34 are much worse. This may not be SIIG or HP's fault at all, but just a stupid industry wide specification for ExpressCard.
Also the drive did not work AT ALL on Win7 Pro 64bit when I used the then recommended 1.0.14.1 driver. I called SIIG support and they eventually emailed me a link to use the 1.0.15.0 driver, but absolutely no "how to do install it" info. I have been computing for many years and tried several of the 'normal ways' before I got it to work. (Sorry, but that was 12 days ago and I don't recall how I finally did it. My mistake.)
Summary. It works, but not ready for Prime Time.