In HiveSigner, you have to give your private keys, which means that your private keys are stored in a database on the HiveSigner server (which makes them vulnerable to being hacked or leaked). With the HAS protocol or Keychain browser extension, it's your device that performs the transaction with the HIVE blockchain, which means that your private keys never leave your device and will never be shared with an application.
In HiveSigner, you have to give your private keys, which means that your private keys are stored in a database on the HiveSigner server (which makes them vulnerable to being hacked or leaked). With the HAS protocol or Keychain browser extension, it's your device that performs the transaction with the HIVE blockchain, which means that your private keys never leave your device and will never be shared with an application.