Hi @Husain,
No, the user ID is not available to the custom visual sandbox. The two visuals you've linked are also certfied, which means that they aren't doing any comms to external services (as this is something that in not allowed for certification).
I've not researched the act of commericalisation of custom visuals very heavily, as my intentions have always been to open-source them for others to learn from.
My guess would be that license checking is handled internally to the visual, possibly using a process like the one proposed here. If it is, then it's possible that the number of users licensed is entirely honour-based from the customer side, but the vendor will have terms of service that the customer could be in violation of if they are found to be exceeding this. Licenses might possibly have expiry dates and be issued on a regular basis to mitigate this also.
As MS leave the handling of commercial costs to the vendor (and some probably do handle this using external services), I'd suggest that if you want to know specifics about how this is being managed then you are probably best reaching out to the developers of specific visuals that you aspire to emulate to see if they are willing to share details on how they handle it.
Regards,
Daniel
