Custom Audiences.
We may use marketing tools such as Facebook's Custom Audience and Lookalike Audience program that enables us to display personalized ads to consumers with characteristics similar to those of our existing eero customers. To determine relevant characteristics of our existing customer base, we may process your email address and/or phone number through Facebook’s “hashing” local browser application that converts this information to a string of alphanumeric data that is then sent to Facebook to enable Facebook to identify other Facebook users with similar profile characteristics.
The above is from their privacy policy. I do not wish to have any info of mine to be given to FaceBook. I have been avoiding FaceBook all my life - I have never had a FaceBook account or any account on anything related to FaceBook.
However, with the above info, my info (even if false) is still being given to FaceBook. Giving fake info is useless here because they have my IP address, my devices' MAC address, IMEI etc. which they can collate with all other "fake" info I have provided to other services/sites/apps and identify my real info/location/etc.
Yes, the lines immediately following the above quoted text does say I can opt out of this collection later, but the damage is already done. I can opt out of future collection, not the one that was already collected when I set up my "not technically an account or a registration but just a login ID".
You say "Then buy something else." Well, that is where I started my post - almost all of these mesh routers do this online account setup; and I was trying to see if there was that something else that I could buy that does not do this.
You might also counter by saying I have an Airport Extreme and that my info is with Apple with my Apple ID as my "account". I trust Apple more than I trust other corporations. And Apple does give me the option of not sending any info (analytics, trouble-shooting, diagnostics, logs etc.) to them right at the time of setting up itself instead of collecting first and later giving me an option to opt out. And they still provide firmware updates even if I chose not to provide them with that info.
Cheers