I agree, the 10k steps is just a marketing myth someone made up. None of my doctors have ever told me to walk a certain number of steps. Steps can vary. How fast are you walking? Are you walking up or down a slope? Are your legs long or short? Sure, walking 10k steps is better than 0 steps, you don't need a fancy study to show that. The whole point is to get off your couch and get your heart (and other muscles) working. It's funny when I see some people get up every hour when they don't reach their goal and walk around in circles to reach a magic step limit. Sometimes while eating a snack at the same time.
That's why even Google Fit follows the AHA recommendation to go by MINUTES. "Moderate" Exercise for 150min per week or about 30min 5 days/week or 20-30min per day. Ofcourse "Moderate" is hard to measure since it is hard for one to know if they are exercising enough and it is easy to cheat yourself. There are various definitions like heart rate of 180-(age) or exerting yourself until it is hard to hold a conversation or sing or when you start sweating. Ofcourse, none of these are perfect measures. Maybe you have a poor lungs, maybe you're in a hot room, maybe your on blood pressure medication that lowers your heart rate. The fitness watch makers invented "Active Minutes" to based it on your heart rate and a zone based on your max heart rate. This is a far better measure to go by than steps.
Sorry for the rant, I find it annoying when marketing hype confuses the general population with actual clinical guidelines.
How about a review comparing heart rate accuracy both resting and while exercising?
I remember comparing many and settling on the fitbit as being fairly accurate. My main use is while I'm exercising to make sure my HR is in a certain range I made up. Just for fun, I also try to see how accurate it is at guessing my carlorie burn. I find it is way off and thinks I burn a lot more than I do. If I ate as much as it thinks I burn in a day, I would gain alot of weight. I think there's even a clinical study that showed this. Ofcourse it's hard to know what your BMR is, but it's obvious the the formula doesnt work for everyone. I have to lower my height by about a foot to get it close to my actual calorie burn. I am getting ready to dump the fitbit because it no longer automatically syncs with my phone it literally will take over an hour to do a manual sync sometimes.