For starters, Odenza's certificates do have an expiration date, which will be approximately 30 months from the date you request the voucher. You'll need to complete your trip by that date, which means you'll have to register your voucher with them a minimum of 60 days before the expiration date, but sooner is even better. Our own certificates won't have an expiration date.
To register your Odenza voucher, you will need to pay a $100 deposit, which will be applied towards the taxes & fees of $40/night when you finalize your booking. It's also fully-refundable should you decide at any time not to book. On our own program, there won't need to pay a deposit upfront. However, the taxes & fees on our program will be a little higher (probably around $49/night).
On Odenza's program, you will need a major credit card, as they don't accept debit cards. You can use either a credit or debit card to book our program.
Finally, Odenza only allows you to redeem one voucher with them every 24 months. And the don't allow group travel (ie, using multiple vouchers to book multiple rooms for a group of people traveling together. We plan to get rid of both of those restrictions, unless otherwise required by our parters.
You can view a sample Odenza voucher here.