What are goerli TESTNET ETH tokens?

As a seasoned professional in the realm of cryptocurrency and finance, I must inquire: Could you elaborate on what Goerli TESTNET ETH tokens precisely entail? Are these tokens replicas of actual ETH tokens, intended for use on the Goerli test network? If so, what are their primary purposes? Are they solely for testing smart contracts and decentralized applications before deployment on the main Ethereum network? Furthermore, are there any key differences in functionality or usability between Goerli TESTNET ETH tokens and those found on the main Ethereum blockchain? I would appreciate a concise yet thorough explanation to gain a comprehensive understanding of this subject.