It works well, but you have to figure out the markup and dynamically styling the images are difficult; For example, to make darkmode work, I have to apply css filters over the generated svgs.
It also doesn't show anything if javascript is not enabled, so I duplicate the contents into a noscript tag as part of my site's "build" process so users can at least know a tikz diagram is supposed to be there.
I have an entire custom build process though, so that might be why it was straightforward for me to incorporate it.
How big does the resulting binary get?
edit: oh, looked at the demo on https://tikzjax-demo.glitch.me/ and it seems like it is just a couple MB. Not bad.
You also won't have something nice like $$ or \[ \] and will have to put the
<script type="text/tikz">
\begin{tikzpicture}
...
\end{tikzpicture}
</script>
tags directly in your markdown, if that even works.