The open and close UX interferes with the site’s UX (on my site for example opening and closing the drawer can interfere with the home, menu links causing a page transition) Features-wise, it’s the best tool out there - there’s options for public/private/closed groups, threading annotations, annotating PDFs and more. There’s also a robust ecosystem of tools to follow users, monitor site annotations etc.

And you can play around with it yourself on this demo page I set up. Some observations: