It's really outside my area of knowledge. The best advice I can give is to read up on the reviews of the device (as many as you can find), and make your own determination as to whether you'll be able to capture HDTV. I just don't know if the HDMI output from your cable box is still protected.
The device does come with a input dongle that allows you to connect via Component, Composite, or S-Video, so using one of those outputs may work for you.
P.S. you linked to the Open Box version of the device. I'd be wary of that as it may not actually contain the input dongle. It should, but it might not.