1. if they are registered with GST, they should probably start maintaining inventory and for that,this device is not useful.
2. if they are NOT registered with GST, they can't even bother with this because nowadays UPI is becoming the norm and all sale gets recorded there anyway.
this would only serve the niche of "not-registered for GST and using cash" but knowing how big india is, with the right marketing, this should blow up in a good way