Customer's have succesfully deployed both vBNG and vVLNS in productions.
There is no specific requirement to run vBNG other than Subscriber scale licence. If can spin up a vMX; you can use the same to test BNG features.
Starting in Junos OS Release 17.2 with the appropriate vMX PREMIUM license, you can evaluate vBNG without a vBNG subscriber scale license for 30 days. After 30 days, you are limited to 10 subscriber sessions.
You can contact Juniper is you need Licence for production.
Else you get 30 days everytime you re-spin the vMX which should be enough for testing.
If you have some specific questions please let us know.