to be clear, Juniper has two different layer 2 configuration setups, one released on the MX and the other used by the EX and SRX series devices.
The EX9200 is the exception where this platform uses MX layer 2 configuration.
The vSRX does not fully implement layer 2 features.
So your usage of the vMX as a test or study model should take into account what you are preparing to implement in production and on which platforms. Or what certification track you are studing for.