I used to use just the app, now I wear the armband and pay a monthly fee.
Honestly, I don't actually listen to it when it tells me to rest, because a lot of those times I'm at work and am unable to rest at the time it is telling me to. So I rest when I can.
I would advise to use the app and see how you get on with that, it doesn't give you any pace points, but does give a daily number and some advice. I hope that helps xx

Can you tell a noticeable difference when following its suggestions?

I have found the Spoon analogy is very helpful.

https://www.makevisible.com/

Visible - Activity tracking for Long Covid and ME/CFS

https://www.makevisible.com/

What is a visible device?