What's the point of a hardware wallet if you still need permission from some third party to be allowed to use your coins?
Exactly this. I will never trust a device that someone else holds the key for - ever. This is a fail in all respects & I urge everyone to avoid it until they change this anti-feature.
Trezor for the win.
we also have a single-sig option coming soon.
note it's considered (eg by coin-center) that blockstream.com/green is non-custodial because you can spend by yourself after a time lock (with the default 2of2+timelock config).
there is also a 2of3 config (create sub-wallet, pick 2of3) which allows you to spend immediately.
The function of the server key is to have multisig enforced 2fa to protect your funds.