It is very annoying that clicking the reader mode button sets scroll position to the top of the page, and the user is forced to scan for whatever sentence they were on before they pressed the button, or use ctrl+f if they know about it.
The longer a page is, the greater the theoretical benefit of reader mode, and the more time the user has to remember it exists. But the farther you are into an article, the greater the cost of switching to reader mode Consequently, reader mode is only ever worth it when the remaining text is so long as to justify the whole, "select and copy a few words, switch to reader mode, ctrl+f, ctrl+v, escape," dance.
There is no good reason for the cost to scale this way!
As a user also has the option to switch on the Dark Reader addon for the current domain with just two clicks, I never cross the bridge to reader view and as a result wind up wasting a lot of CPU time and electricity. (Dark Reader is infamous for being an enormous performance suck, even after the page is loaded.)