What is it? I haven’t and I thought I’ve tried everything

I have not

I have not. I have a Garmin watch that does the same thing and doesn’t require a subscription. There are much cheaper options out there with similar features.

Let me know if you are looking for some recommendations. Pre MG I was a gym rat, marathon runner, health coach. Now I adapt my fitness to my MG capabilities and use the training features on my watch to track workouts, quality of my sleep, step counts, body battery charge, heart rate alerts and pulse oxygen levels.

I have not might try it out one day

It's like a fitness tracker, except it monitors your fatigue. So after a while it will have a profile of your energy and can warn you if you are expending too much and should slow down and rest