The Jade is nice IMO, but, as a wallet, the security model is dependent on a remote server run by blockstream. The Jade can, however, be booted into a "signing device" mode, where you temporarily enter the 12/24 word seed phrase, sign/send a transaction using the camera, and shut it down with no data retained.
Discussion
I will also say that the Jade has a tiny tiny screen. So if you use it in QR communication mode (vs Bluetooth paired with Green Wallet), it can be frustrating sending the signed transaction back to the device reading the QR code.
Say more about the remote server run by blockstream?
Non-technical breakdown: The Jade uses your numeric PIN code, a secret stored on the Jade, and the blinded Blockstream server secret to spend the bitcoin.
Technical summary: The Jade has no secure element. It stores the seed information encrypted with a secret on the Jade device. But the Jade secret is also encrypted. The user logs into the Jade with a PIN code. The Green wallet software will then reach out to Blockstream servers to retrieve the decryption information for the Jade secret. The Jade secret is decrypted, and the Jade can now spend the bitcoin.
Actually, I'm not entirely sure if the "Jade secret" is the seed itself, or is simply used to decryption of the seed.