I have a Final card. You have three options:

1. Use your real card number. I never do this. 2. Use a merchant-locked card number. I use this commonly for online pizza and other online shops I don't trust much. Once a merchant uses it, only that merchant can use it. 3. Use a one-time card. The number is used once and disabled. Good for one-off orders or skeezy purchases.

Overall I've been pretty pleased. I think the idea that card numbers should be disposable is awesome.