Some feedback on cmdliner from a late adopter (I know it’s off-topic, but we’ll be ok):
I don’t understand the cmdliner type machinery, but I get by by using past projects as templates and sources of examples aka copy-paste. Also, I avoid using & completely (I forgot what it does except that it’s trivial).
Once I have a template for a CLI implementation, most of the time is spent figuring out how to express the type/format of a command-line argument. Maybe a cheatsheet would be beneficial.
The feature-completeness and the output of cmdliner are amazing.