I've used Jio-Fi M2S and JMR815. Don't buy JMR815 it's the worst Jio-Fi. You can buy M2S. I think it's the best jio-fi. Battery backup is decent but, the battery is not good. There are some cases where battery got bulged after 6-8 month of use. Don't know if they've fixed this issue.
I also want to buy Airtel hotspot but the cost is around ₹2500. Yup it's true Jio-Fi device (also jio phone) is horrible.
I've watched YouTube videos on 144p without buffer. Thanks to Jio