In addition to Polar and Suunto, Finland also hasย ลura on the ring side. I tested their V1 long ago, and was impressed. The ring form seemed to allow for better measurement of heart rate to the point of reliably using HRV for "readiness" predictions, and temperature to the point of possibly being applicable for basal temperature for ovulation detection, something I doubt any watch could do as accurately simply because of form factor. Then again, I haven't tracked progress lately.
If you are more concerned about your money and data staying in the EU than the brand, I'd also suggest a used device supported by Gadgetbridge; I used to have good luck with used Mi Bands (newer models may not work, or at least need installing the default app and digging up a code).