At least for me the prompt isn't a one time thing, unless you consent to enabling telemetry. I get asked whether I want to enable it all the time when logging in.
Yes, you can disable it forever [1]. Oh and there's actually a tiny "skip" on the nag screen in dull contrast, more user hostility. It's the concept I object to, though: If I pay for it, I should not be the product. And a privacy notice on something that's by definition supposed to be private.
1. Control Panel -> Info -> Device Analytics.
https://www.reddit.com/r/synology/comments/8mdioc/device_ana...