Can't find a lot of detail on this deal, but says you just pay $10 and get a $20 voucher credited to your account.
So my guess is it can be used on sale items etc.
Also no expiry date I can see, just "limited stock"
Have received my voucher now. Expires in 2 years. Can use on anything including sales.
Appears to be sold out ; "sorry, all alocated"