I use it but you have misunderstood what it does. It builds a model in memory and then you can use that to do other tasks at build time. It doesn't persist the model in a form that the app itself can use to start up faster.

See here:

https://github.com/remkop/picocli/issues/539

Although looking over that issue, it looks like maybe reflection was never proven to be the source of the slowdowns.