I have stubbornly not migrated. I expressly advise people who value their privacy to not to get NEST now for this reason.

EcoBee is a great HomeKit-aware thermostat and you don't need to sign up to their account to use it (although it'll keep nagging you to, it's not required).

Was forced to when I wanted to add their cloud monitoring service. The payment system is now Google's.

I sold all of my Nest thermostats and moved to Ecobee.