This application don't send your personal data to any third-party services expects Telegram.
Push-notification-server uses for sending messages from telegram to bot. This server uses Google Firebase Messaging to send push notifications to device. Messages don't stored on the server.
You need be careful and don't leave Telegram client opened with bot in contacts nearby other people.
It is forbidden to use the program in order to spy! In case of unauthorized access to the bot and your personal data, I case of data or device corruption as a result of using this app author of the app does not bear any responsibility.
You use this software at your own risk. If you disagree, you need to uninstall the app.