BlueWallet is one of the safest ways you can use Bitcoin if you are not using a hardware wallet or a "multisignature" custody setup.
The wallet is open-source and has been reviewed independently to make sure there is no malware or backdoor.
The developers cannot have access to your Bitcoin wallet.
The private keys that control the bitcoins are encrypted on your phone and protected with a passphrase. To spend money each time you must decrypt your device with your app's password or with your biometrics.
BlueWallet protects you well against non-hacker people that gain access to your phone.
BlueWallet is more vulnerable to malware and hackers than hardware wallets.
BlueWallet lets you create backups easily and securely which let you recover access to your money if your computer is damaged, lost or stolen.