Ask HN: Is an in-page speed reader useful?

A friend suggested I embed an RSVP reader in my blog posts, so I did a floating button in the corner of the page. It uses the Spritz heuristic for the focus letter (letter 1 for short words, up to letter 4 for long ones) but maps back through punctuation, and the timing isn't uniform either. I don't want to bury this post in technical detail, so if you're curious about any of it, just ask and I'm happy to share.

But I'm not really used to speed readers, so I don't know if it's actually useful. What do you think?

And about browser extensions? does a per-site reader still make sense when an extension works everywhere, in theory?

It's on my blog (glitchedcat.com) on any post the lightning bolt button in the corner.