1. The Jade Plus is a big improvement all around. The metal version is a bit weightier and feels nice, albeit less stealthy (it's metal). The nav buttons need an upgrade; currently feel sticky and not very tactile. Screen is great. Cam is great. I want to see NFC next, vs USBc/BT/QR modes.
2. The Jade Plus is for managing offline keys, you still need to interface with Green or other option (like Sparrow etc). Those things must be installed on a computer. #GrapheneOS, especially dedicated, is going to be easier to maintain and more secure than a laptop for this purpose. You can use QR mode to prevent a direct connection between the Jade Plus and the signing interface on the device. The coupling is very loose; so I wouldnt characterize it as "linking your hw with your phone". Plus, this is a dedicated device for this purpose only, not my daily driver.