Curious to hear from anyone with long term success: do these kinds of apps actually work or do they more just make you feel like you’re doing something about it?

They work in that they induce taking more breaks (20/20/20 rule) but they're also annoying in that they interrupt deep focus. If the latter can become a bit smoother about not interrupting deep focus context, then they'll be more helpful.

I used to suffer from pretty chronic eye pain when I was looking at the computer every day for work for 5+ hours. Consciously taking a breaks every 20 minutes has completely the symptoms altogether. Just being aware of how long it’s been without resting my eyes was eye opening (pun intended)