Seperated Jaws

Hello,
Does anyone in the group own or have used Seperated Vise Jaws? If so I was
wondering what could be expeced with their parrallelism and holding? I'm
specifically wanting to use them on my Round Column Mill Drill.

For those who don't know what I'm referring to:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3880884274

Thanks,
Rob