So, I subscribed to Rs.29 plan (59 from next month).
1. I was logged in on windows PC while subscribing (Device-1). Checked that premium content are working. Then closed the Jio Cinema window.
2. Then I used it on Fire Stick #1, premium content working. (Device-2). Closed the app.
3. Then I logged-in and used it on Fire Stick #2, premium content working. (Device-3). Closed the app.
4. Came back to Fire Stick #1, premium content working. (Device-2).
5. Came back to windows PC, premium content working. (Device-1).
Have more devices but it is confirmed that Rs.29/Rs.59 is working on multiple devices (one device in use at a time) like Netflix.