im sure some people find them useful but pretty much everyone i know who own them it's a complete waste of money. My bro and sister in law have them, they also have smart watches, sheets under their bed to monitor they sleep and speed 100s a month on subscription to supplements yet are always tired, ill, or coming down with something. They dont seem to understand that drinking lager every single day and having a horrendous diet is the reason and all the gimmicks and supplements in the world aren't going to magically fix that.
Im not really sure all this over analysis of your health is any good for you. Why do you want to know what your resting heart rate is 10 times a day, or how your sleep was or be reminded to stand up every hour. People are obsessed with it like its a validation as to why they feel shit, when the answer is usually not moving enough, drinking too much or having a shit diet, but people want the justifications without doing the work to fix it these days, just look at how the body positive movement for fatties has stopped now they can fix it with a jab, they didnt want to be fat, they just didnt want to do the work that they need to not to be