At the moment it's much safer than most other CMS's, as there is no admin backend to hack into. A hacker would need access to your actual server to change a Baun site. So hopefully there should be no headaches.
We don't have a demo but http://bauncms.com is built using Baun. Despite having similar features to Pico, this is a complete rewrite using modern PHP standards. I sold Pico a while ago and sadly the project seems dead. I'm hoping to go much further with Baun.
I think you're talking about a carousel (showing multiple slides at the same time). This is technically an "image slider" so is designed to only show one slide at a time.
You could just create a static HTML site yes, but getting it generated for you from Markdown files is super handy. To generate it on the fly it needs to be powered by some kind of server (e.g. Node, PHP, Python etc). Nodejs was just a good choice of platform for this kind of thing.
Raneto is secure because it doesn't have any kind of interface that can be hacked (e.g. a login page). To make changes to Raneto content you need to have access to your server file system.
Thanks. I actually created a flat-file CMS in PHP called Pico (http://picocms.org) so I built on some of the lessons I learned creating Pico when building Raneto.
I did consider simply building a KB with other static site generators, but I wanted something specifically designed for Knowledgebases and easy to setup and use.