I don't think any of them do Blood Pressure, so strike that.
I believe all the major brands require you to create an account on their phone app which is also an account on their web site. Garmin has desktop software for a computer, but the watch still sends the data to the phone app which sends it to the Garmin website. The desktop app pulls the data down from the website. The other major brands are very likely the same way....and for legit reasons.
Even if you create a new email address to use to create the login to the app, you can't be sure the app isn't looking for the local gmail address and/or phone number and linking with that. If you _really_ wanted to be sure you stay anonymous, you'd need to get a different smartphone with it's own gmail address (and maybe not even a phone number). Even then, if you did a GPS activity that started and ended at your house, their website could probably Dox you.
I think most people probably look at it, decide they want the benefits of a fitness watch and just accept that someone could be mining the data.
FWIW - I've have a Garmin Vivoactive 3M for running and give it a huge thumbs up.