Great concept, but for those of us who believe sites should be responsive, it may not be useful.
The page on which I tried the TOC lost its ability to respond to the width of the device displaying it.
Perhaps this is a problem with only the theme I'm using (Gridly), because the shortcode didn't work at all. I had originally set the required headings to 10 and inserted the shortcode. When I didn't get a TOC, I reduced the requirement to 4 and removed the shortcode. That gave me a TOC... and an unresponsive page.