I talked my wife into switching, some google app to drip. She loves it! Helps so much at the doctor's office and helps predict when to expect monthly pain.

And

https://f-droid.org/packages/ch.nilsgrob.android.bluemoon

I do, because I have chronic health issues that require me to monitor these types of variables. I also use it to predict my next period so I can prepare and so I can be a bit kinder to myself. I use Drip though so everything stays on my phone and that bunch of people won't mine shit.

My memory is so bad I definitely need to write it down if I want any hope of knowing where I'm at in my cycle. I also used to try to track more symptoms, which helped me learn a lot, but now I just do the minimum. A physical notebook or even notes app would work just as well, but I just do better if it's on my phone and like the visual calendar. And also use Drip so not worried about the data getting out. I agree you don't need any fancy apps, but don't like the implication in the article that tracking at all is useless.