I don't think that scalability is a pertinent criterion for firewalls because they're hard-coded by the ASICs that go into them. When we rent a firewall to a customer instead of selling one, that customer has an upgrade path available. In this regard, it is scalable because we can switch them to a larger model if they outgrow it. Otherwise, it's limited by the ASIC.
Firewalls Upgrade Path Reviews
Showing reviews of the top ranking products in Firewalls,
containing the term Upgrade Path

reviewer1385226 says in a SonicWall NSA review
Solutions Architect at a tech services company with 51-200 employees