I think it's a bit more nuanced than just "don't depend entirely on third party APIs," rather make sure that your API provider benefits from your use of their services expanding. [1] Issues only arise when your success comes at the expense of the API provider, whether thats by poaching a potential audience or otherwise.
I just noticed in the FAQ it states, "...several fields have been renamed of course." If I'm understanding this correctly, any real-world conclusions you draw will be completely meaningless, as we're essentially working from a mislabeled dataset.
Honest question: What's the value of this service? It seems you seem to suffer with any volatility: the exchange rates would be a constant drain on your net worth. Without any volatility, the service basically does nothing.
There doesn't seem to be any benefit, other than maintaining a minimum or maximum balance on your account. Perhaps this is useful for merchants who want to accept BTC without the risk of holding an excessive amount of BTC. Hmm. I might have just answered my own question.
[1] https://mkwng.substack.com/p/whose-problem-is-this