I don’t have a formal diagnosis of ME/CFS yet, but fatigue is my most disabling symptom right now. I’ve used an Apple Watch for about 6 months now and it has been huge for helping me pace! I often suddenly crash so I used to accidentally overdo it all the time, but I found my general limit (in terms of steps). I set that limit as my “goal” for daily steps on my watch so I can easily keep track of it during the day. My watch face shows me how close I am to the goal all the time, so I can look quickly down to see how many steps I’ve used up and how much I have left. It helps me plan better to make sure I’m not doing too much or I save my steps for an activity that I know is coming up. Since doing that I tend to not crash suddenly and have a more stable energy level. I also use it to track my water intake, heart rate, sleep, etc., all things that are useful in managing my conditions. I also frequently check my heart rate when doing any sort of activity to help me gauge and make sure I’m not pushing myself too hard. It’s kind of hard to explain - I hope that made sense! Let me know if you didn’t understand. But long story short, it has definitely helped me. I think most fitness trackers would be able to do most of these things.