Mobile Chrome has some broken heuristic to prompt it. I never know when I can expect it to appear. Sometimes the website already looks good and it appears. Sometimes it looks horrible and it does not appear.
Also sometimes this "reader view" looks worse then the original. It has too small font for my taste. When you pinch to zoom it looks like it changes the font size, but also the viewport. So it is entirely useless.
I expect that it will be removed (or replaced) in future.
I would still argue that its function is different than the "reader view" functions of other browsers, but it does have it.