The Tester Approves thread (see first post)

Not sure how appropriate

Highly inappropriate. Everything after the "?" in your URL is unnecessary. The URL might go to a 404 error when the product runs out, is discontinued, or CRC just decides it's not worth offering. Strangers from the future will then have no idea what you're asking, just as I can only guess now unless I bother to click on the link and try to decode your enquiry. Put your question in plain text.

What if any difference does this finish make

Depends what finish they use. Bright silver on cassettes is usually nickel plating, which is used for corrosion protection and might offer lower friction than the base metal. The ED black is also a corrosion inhibitor, but it's softer than nickel plate. In practice, on a heavily used bike neither will make much more than a cosmetic difference.