I switched from MathJax to KaTeX earlier this year for my blog. So far, it has been working out well.

The only feature I really missed was the ability to use \label and \eqref for equation referencing, since KaTeX doesn't support these commands [1]. I worked around this limitation with a small custom setup defining my own \label and a custom \eqnref (not exactly \eqref though) [2].

Another thing that bothered me a little was that the KaTeX autorender extension does not recognise \begin{align*}, \begin{alignat*}, etc. as top-level delimiters by default [3] but this was trivial to fix by customising the set of default delimiters [2].

I know KaTeX supports server-side rendering but I don't use that yet [4]. I still use client-side rendering. Despite that my maths pages [5][6] render quickly since they are usually small, with only a single reflow from the initial load to the rendered page, without the continual reflows or jitter I used to see with MathJax. Overall, I am quite happy with the switch from MathJax to KaTeX.

[1] https://katex.org/docs/supported.html

[2] https://github.com/susam/susam.net/blob/0.3.0/layout/include...

[3] https://katex.org/docs/autorender#api

[4] https://news.ycombinator.com/item?id=44615271

[5] https://susam.net/mutually-attacking-knights.html

[6] https://susam.net/zigzag-number-spiral.html