The cable is only 9" long, so to enable you to knit completely in the round the actual needle size has shrunk to around 4 cm. See the picture below to give you an idea of the scale.
The second photo below shows how you knit completely in the round. The only exception to this is for the heel flap (for a top down sock) and the toes for toe up or top down socks. I usually swap to dpns or Magic Loop for this bit. It's quite easy to adapt a dpn or Magic Loop sock pattern for use with these needles, but you do have to do a little bit of fiddling about when it comes to the heel and toe. I have actually just written a basic top down sock pattern specifically for use with 9" circular needles, but it's still very much in note form and I think at the moment only I will be able to understand it! ;)
Sadly at the moment the only outlet in the UK appears to be Sarah at Brownberry Yarns. I think she has been inundated with requests for the smaller sizes and has now consequently sold out, however I'm fairly certain you can pre-order from her if you're desperate to try them. Maybe I should keep this quiet, so Shhhhh don't tell anyone ;)
If anyone knows anywhere else that sells them in the UK please let me know, or even an overseas stockist with reasonable shipping costs to the UK. I could do with a few spare pairs! :)