Do you know the reason for the larger attack surface of Keystone?
Discussion
It's basically a cell phone without the cell phone. The touch screen is one attack surface. The Q also has dual secure encleves.
I also prefer the way the Cold Card allows you to chose BIP39 seed phrases for the passphrases. This makes typos less likely.
They Keyboard on the keystone is terrible for someone with thumbs as fat as mine.
I also prefer the Seed XOR standards to Shamir Secret Sharing. SSS is not as standardized, but this is super geeky advanced stuff.