I can't speak for that particular service, but in other similar ones I've looked at and used in the past, you're paying for a certain number of IPs _at a given time_.
So, for instance, they have a pool of servers that have 1000 IPs available. Your account allows connections to go out over 2 of those at a time. If something happens (like one gets banned by whatever service you're scraping), you can get a different set of 2 IPs and keep moving.
While you're still paying a relatively high price for what you're consuming (predominantly bandwidth in this case), you're paying for the flexibility.
