See VSX R80.40 Administration Guide p.119:
VSX Licenses
Each VSX Gateway or VSX Cluster Member requires its own license, bound to the VSX Gateway or VSX
Cluster Member IP address. Each VSX Gateway or VSX Cluster license covers a predefined number of
Virtual Systems (3, 10, 25, and 50) and these licenses are cumulative. The VSX licenses are applied in
addition to the Security Gateway license (container and Software Blades).
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So a vSwitch only costs much memory, but no license...
CCSP - CCSE / CCTE / CTPS / CCME / CCSM Elite / SMB Specialist