The web-site for it is very "odd." You don't even seem to need to confirm you own Windows 8 for it to send you a key, just an e-mail address...
No idea if it is one-time use either or if when you reinstall you can re-use the same key to activate the DVD codec etc.
I do know that it is £7 full price. Which is a lot of money now that the DVD decoder doesn't even work in Media Player.