Locking apps with fingerprint or face have one major drawback, which is that anyone can unlock your device when you are sleeping or when you are unable to fully realize what you are doing (the influence of alcohol or drugs). Some manufacturers advise turning this option off when going to sleep, just to prevent abuse.

If you lose your smartphone, you can always respond by using your backup and recover your wallet on another device. Then you just move coins to a new wallet (not only a new address in the same wallet). This way your old wallet will be empty, so there will be no harm even if someone manages to get access.

Mobile wallet is safe for small amounts, maybe $x00 or something like that, just be sure to protect your phone from malware. Be careful with every application you download and keep a close eye on security (install security patches/updates for your device)