Trezor is open source, and you could generate your recovery seed on a computer and import it onto your hardware wallet. I believe Ethereum and some other crypto

Trezor is open source, and you could generate your recovery seed on a computer and import it onto your hardware wallet. I believe Ethereum and some other cryptocurrencies prefer to use deterministic signatures on transactions, so in theory it's possible to check that all of the signatures generated by the hardware wallet match the expected deterministic signatures so you can know that the wallet isn't secretly leaking information through the signatures it's generating.