Yes, multiple subscriptions for the same item are managed independently from one another.
If the same callback method is used and you still need to distinguish the two subscriptions, you could add custom attributes to the two NonVisualTable instances.

If you have a lot of items, the screen update activity is more likely to become the main bottleneck.
In this perspective, using one multi-item table or multiple mono-item tables does not change the performances.
Performing 100 mono-item table subscriptions in a burst does not cause 100 HTTP requests to be issued to the Server, as the requests are batched; so, the performances are not expected to degrade.
Resubscribing upon page changes is then very light, as shown by our Grid Demo.