You don’t actually have to use the app to backflush. You can just do it manually. The app is more convenient than flipping the lever a dozen times though.
What data do you think they're "harvesting"? If they're counting how many shots I pull and judging me by my choice of brew temp, I can live with that. The app adds a lot of convenience and saves having to have some sort of UI or manual control on the machine itself.
Why do we collectively continue to give up privacy to spare us the most innocuous of "inconveniences"?