Trust wallet is good but not completely reliable, it is only safe if your device is safe, once someone get access to your phone or laptop, your wallet can get hacked; it is a closed source hot wallet.
Your statement saying "it is only safe if your device is safe" is true when talking about a trustworthy open-source wallet like electrum, not about trustwallet.
As you know trustwallet is close-source and we don't know how the keys are generated. So, it's possible that you lose your fund due to vulnerability in trustwallet while your device is safe.