I'm not seeking to criticise this product, I think this is a great development.
But, for almost all people this is shifting from one kind of "trust me bro" to .. another. We're not going to be able to formally prove the chip conforms to some (verilog?) model, has no backdoors, side channels, you-name-it. We're in the same place we were, with the same questions. Why do we trust this and the downstream developments? Because we do.
I know people who worked on cryptech, and I definitely had trust in their work, personal commitment to what they did, but that's "who you know" trust. The non transitive quality of this kind of trust is huge.
To be more critical my primary concern will be how deployment of this hardware is joined by significantly less benign design choices like locked bootloaders, removal of sideloads. To be very clear that's a quite distinct design choice, but I would expect to see it come along for the ride.
To be less critical, will this also now mean we get good persisting on device credentials and so can do things like X.509 certs for MAC addresses and have device assurance on the wire? Knowing you are talking to the chipset which signed the certificate request you asserted to before shipping is useful.