I used Reddit Is Fun for over a decade. It made Reddit usable on mobile for me. The UI for the mobile site and the official app make poor use of screen real-estate, IMO, and are designed to force you to continue scrolling and scrolling and scrolling. They're attention vampires.
RIF and other third-party apps had much cleaner UIs, that made it easier to find the content I was actually interested in, hide content that I didn't care to see, and interact with comments in a way that made sense for me. It was also easier to customize my notifications so that I would only be alerted by things I cared to be distracted by.
Without the third-party apps, I've reduced my Reddit usage tremendously. I used to spend probably a few hours a day just reading through Reddit, but now that I can't do that from my phone in a way that works for my use-case, I just simply don't use Reddit as much anymore. I only ever access it from my laptop now, and I only ever use my laptop while I'm on the toilet.
My Reddit use has been reduced to literal shitposting. Fuck Spez.