If you're talking about Mathew Krater, I'm not sure you understood what he was saying. Coin joining is not "unsafe" and he wouldn't have said that at all. He would have instead criticized the method being used, Trezor and the people behind this implementation saying they went against the ethos of Bitcoin.
Trezor and Ledger are generally both not great options "ethos"-wise for hardware wallets/signing devices.