Packages are one-time payments and your quota will not expire. You can buy an amount of conversion credits and use them whenever you like ("pay as you go").
BEST VALUE
Subscription
$10.00/month
1,000 Conversion Credits
$0.0100 per credit
Monthly billing
Up to 50% savings
Automatic renewal
Subscriptions charge you every month for a fixed amount of conversion credits. Not used credits do not roll over at the end of the month. In exchange they are up to 50% cheaper than packages.