The Monerujo app is not the official mobile app for Monero. Rather it is a community developed open-source mobile app. It is considered by the community to be safe and secure, and is one of the mobile apps that is recommended by the developers on the official Monero site.
This is because it is open source software and you can view the source code in their GitHub repository. Moreover, I can confirm it is easy to use as well.
It’s also a lightweight wallet solution since it doesn’t download the entire Monero blockchain. Instead it uses remote nodes for synchronization, which works quite well. The Monerujo stores your private information only on your own device, keeping it as secure as possible for a mobile wallet.
You never have to worry about your private information being available on a company server. It’s a great balance between security and performance.