I'm taking advantage of an ordinal block explorer to by giving the envelope the ordinal identifier "ord" so the SHA256 hash is picked up on the ordinal block explorer where my app can read the hash.
And regular block explorer can show OP_RETURN data.
Even though I am using the ordinal envelope and using an ordinal block explorer to read the data, this is not an ordinal in a traditional sense. Every user on my app will write 1 ordinal as a registering function for my app. It will not clog up the bitcoin blockchain and will not spam the bitcoin network. Gas fees will not go up because of my app, don't worry.
Bitcoin user will be impacted if your application is popular enough. And if your application is centralized, i don't understand why you chose not to use either email address or phone number.