We've been using openresty in production at vwo.com at our edge nodes for quite a few years. It's really fantastic, allowing you to write custom logic and embed it within nginx itself, making things super fast.

The only real disadvantage is the lack of a good library ecosystem within lua and openresty. Over the years, as we moved some more logic to edge because $reasons, we ended up rolling our own libs quite a few times. Documentation can be made much easier as well.

That, and the occasional limitations of Lua as a language.

Overall though, quite an awesome project.