Now I have this blood pressure monitor device that doesn’t work without a logged in app and is a paperweight. I’m lucky I never invested into their ecosystem of health products. Lesson is no matter how popular a brand is, there is no guarantee they will be around. I’ve lost all my health data and there is no way to get it back.
If you can. Medical devices are particularly nasty: there may be only one or two brands on the market that do what you need, because such devices understandably require extensive certification. If the only available option requires an app, you’re stuck. If you need something that meets other legal or professional certification requirements, you might also have very limited options.
For just about anything else, I agree that there’s probably some alternative to an app-locked device, although some level of convenience tradeoff may be necessary.
One company that I can recommend is Withings. They do have an companion app, but a lot of devices do work on their own, and when not, they work with Google Fit or HomeAssistant, though probably due to that fact the products are pricier.