I have been using it for 7-8 months.
And my experience was fabulous. It contains a lithium ion battery and you can operate it for a long time ( 7-8) hours continuously.
Its camera is not that much mind blowing as in the front camera you can't even see anything if you are in a room with less than 9W LED light, if you want good photos then you can go out in the natural sun light and click average quality of photos.
But in the price of 1500 the camera is nice. It comes with KaiOS 2.5, I have never heard about this OS but you can say that this OS stands between Android and normal keypad OS. It have many applications inbuilt and You can download many of the apps here like-
JioSaavn, YouTube, Facebook, myjio. JioTV, Jio Cenema, etc.
My EXPERIENCE: -
In my 7 months of experience, I use it for listening music and its speakers are just outstanding they are a way better than the new smartphone available in the market, they are just too loud, I also use it for watching movies in the jiocinema app, many new and old movies are available there.
It also comes with google assistant, I have seen this in just the Android apps, what the problem is you need internet for each small thing but as you know that jio provides us internet connection in very low price, so there is no worry of internet.
You can also download jio switch through which you can transfer files from your other phones into it.
It contains a storage of 4 GB which is very much for a keypad phone, because other keypad phones come with just a storage of 100KB or less.
It also have a large screen as compared to other keypad phones, in which you will enjoy watching movies.
My final suggestion is To buy it as it is worth 4K and it is coming in just 1500.