I'm not a security expert, can someone explain to me how this product is used and why it's worth $1000 a month (or even more)? What's the alternative?
The details depend on how much the of advertised scan data enrichment they do, but you might for example ask how many vulnerable cable modems of a certain model there are in the network you are responsible for, and what ISP networks they are on.
To do this on wan you need to run zmap which is considered mean.
On the other hand, if you have a small subnet, say, less than a /24, you might as well just nmap it yourself, and then you're also guaranteed to have the latest possible scan.