Withings is the king of non-invasive home health tech, giving me tons of data and insight into my own health, all automatically synced to my phone, without the need for constantly thinking about or entering data into my phone manually. I will say, while Withings succeeds in design, they've recently started falling behind other products like the Apple Watch when it comes to data accuracy and reliability, with questionable data on features like the ScanWatch's heart rate monitoring and BodyCardio scale's body fat monitoring.
Withings Sleep: might take some time to calibrate based on your mattress size, but overall incredibly useful data. It tracks REM sleep patterns like every other sleep tracker, plus minute-to-minute heart rate, all without needing to wear anything, and doesn't need to be charged since it's wired into an outlet. Truly seamless and non-invasive health tech. Hoping that they add HomeKit/Matter/Thread support instead of the outdated IFTTT support.
Body Cardio Scale: it looks great and the weight data is accurate, but that's the easy part. If you're paying anything over $60 for a wifi scale, you're probably looking for more than just weight data. The heart rate data is beyond inaccurate and useless, and the "vascular age" is so obscure and dry of explanation that is also has no purpose. The body fat data is pretty inaccurate, showing my body fat % as 5-10% lower than DEXA scans that I've done, which is the main reason why I've been hesitant to upgrade to the newer Withings Body Scan scale. Would be cool if they added a phone camera based body fat measurement feature like Amazon Halo or Spren, to help cross-reference and substantiate the scale's data.
ScanWatch: I like that it has most of the smart-watch health tracking sensors, with a week-long battery, beautiful retro look and no interactive screen (sorry Apple, I don't want a mini-phone on my wrist when I have a real phone in my pocket). The problems are in the accuracy and reliability of the data from those sensors. The step tracking is very accurate, but any heart-related data is questionable at best compared to the Apple Watch (see TheQuantifiedScientist on YouTube), and with Apple rumored to be adding blood sugar and blood pressure monitoring in the future, I can't see myself sticking with the ScanWatch for much longer.
BPM Connect: Useful data when set to triple mode (where it runs then averages 3-consecutive scans), otherwise useless and inaccurate data in single mode.