Yes it’s paid, but the quality is worlds above Bing, DDG, or Google. The best description I can make is that it’s what Google Search was about 15 years ago, back when there were no AI results, no ads, no artificially promoted results, and you could vote on results and block domains from appearing in your searches. Back when Google Search was actually good.
So it doesn’t do anything new or groundbreaking, it’s just what a search engine is supposed to be, in a time when every other option has abandoned that goal in the endless search for more revenue.
The nice thing about docker is all you need to do is backup your compose file, .env file, and mapped volumes, and you can easily restore on any other system. I don’t know much about CasaOS, but presumably you have the ability to stop your containers and access the filesystem to copy their config and mapped volumes elsewhere? If so this should be pretty easy. You might have some networking stuff to work out, but I suspect the rest should go smoothly and IMO would be a good move.
When self-hosting, the more you know about how things actually work, the easier it is to fix when something is acting up, and the easier it is to make known good backups and restore them.