> I doubt there is 100% secure device,

you might want to read up on EAL certification. Yes, there is no 100% secure device, but "secure" is about resistance to attack and an actual secure element is very resistant, as well as tamper evident.

u2f-zero could be hacked in 10s flat if you prep ahead of time.

> if an attacker has gained physical access to the primary token ... they don't need to hack it in any way

but they need long term access. with this device, short term access is enough to learn the key and then i can get access at a time of my choosing. i can also learn the counter value and you won't notice that i have gained access.