As for Trezor safe 3, its secure element is close source. Just take note of that.
Trezor 3 Safe is actually using Infineon OPTIGA Trust M secure element and you can easily find it's code on github for inspection:
https://github.com/Infineon/optiga-trust-min the moment you connect to internet im using now Electrum on airgaped laptop and a watch only wallet on my online computer
but the problem is that electrum is btc only wallet when i want to store USDTe
You can also use L-USDT and L-BTC on Green Wallet, that is built on Liquid Network.
i dont really like metamask i have seen many peoples get hacked when they linking their trezor with metamask
Trezor is safe if you use it correctly.
If you don't know what you are doing than you can make even perfectly safe device into unsafe.
I would not use stupid metamask wallet, but Trezor Suite works just fine for what you are looking for.
To expensive for just a code that don't even support all android devices.