The difference between the two options mainly revolves around how you manage your seed phrase and your hardware wallet's interaction with it.

When you choose "I already have a Seed," you're essentially importing your seed phrase into the software. This means the software has access to your private keys, which could be less secure if the device or software gets compromised.

On the other hand, "Use a Hardware Device" means you're connecting your hardware wallet to the software. In this case, your seed phrase remains securely stored on the hardware device, and the software merely facilitates the transaction. The signing process occurs on the hardware device itself, ensuring that your private keys are never exposed to the computer or software, which is much safer.

So, while entering the seed manually is possible, it's generally recommended to use the hardware device for better security. I hope this clears things up!