Correct. It's at best redundant and at worst a phishing service. If you want to develop/utilize a proper ACME client, that's fine, but you need to fully understand your motives for doing so.
Both @webprofusion and I have developed our own ACME clients (with his being far more sophisticated than mine). Even with the great efforts of Let's Encrypt, it's not a simple matter to do, so there should be a functional need if it is to be undertaken.