They aren't different products
It is only different "invoicing tiers". Our price is based on the number of new signups per month. The NATSlite level covers up to 300 new joins/mo for $150/mo. NATSplus is for up to 750 new joins/mo at $350/mo. And NATS is for above 750 new joins/mo at $650/mo. There is a possibility of a couple tiers being added with the release of NATS v4.
None of the levels will stop taking signups at their limit. If you go over it you will simply be moved up to the next tier on your next invoice.
The software is exactly the same.