Generally works really well, occasionally, the download button won't appear, but I've only experienced this with new videos so far. So I am hopeful this is a transient issue.

This works great for me and deserves praise! It has helped greatly simplify note taking (I parse the output to a markdown file and then pass through an LLM).
The button does exist!! You have to open the video description and click 'Show transcript'. 99% of the time it's there in the Transcript box anyway, and when it's bugged and showing 3 dots a refresh fixes it.