As far as functionality goes, it is pretty barebones. The UI is pretty standard. The form editor doesn’t drag and drop which may be a bit cumbersome for non-techy users. However, Contact Form 7 gives the option to edit the html wrappers around form fields; this can be a boon for developers who want to customize their forms in html.
As far as developer access is concerned, there is no API for Contact forms. There is a plugin which exposes the API as a part of the WP Rest API but that plugin’s development is dubious.
There’s also no paid version to upgrade to if you would like more features down the road. In that case, your best bet would be to use one of the more fully featured form plugins like Gravity forms or Ninja forms.