I bought the new keystone 3 pro hardware wallet. At first I was confused because it didn't have it's own dedicated app like the previous versions but it does connect to Blue wallet, sparrow , and nunchuck as a watch only wallet. You have to sign with the device to send funds out. After using it for a couple transactions, I really like it now.

I'm assuming it's the same concept for the seed signer? And coldcard?

My only problem I've encountered is when adding existing seed phrases and keys my balance doesn't show up. Maybe I have to consolidate all the utxos? Or change from legacy to segwit or taproot? I quit fighting it and just spun up another seed phrase and started new transactions to test it out. Seems to work fine.