Thanks for your reply. By "vendor lock-in" I mean that I cannot export my private keys out of any hardware wallet.
Yes, I am paranoid. I sign any transaction offline but I still have to trust the software producers. I don't want to trust.
You can[1], but it's not recommended. However, if you are going to use your wallet with the private-keys outside the hardware wallet device, why even have one in the first place? Your best choice would be to have an air-gapped computer with an offline wallet and a watch-only in your main online computer.
[1] Just get your hardware wallet seed, and in Electrum go to File -> New/Restore -> Standard Wallet -> I already have a seed -> Paste/write your seed -> Options -> Check 'BIP39 seed' -> Next.