Unfortunately, while OpenSearch is great where it's supported, outside of Firefox, the only real support is for in-site-search on other platforms (where you type a site name and then a search string), and not for changing your browser search engine. And it doesn't work at all on iOS even for site search.
So unfortunately it doesn't fix the problem of how a consumer can easily change their search engine to something new on Chrome or Safari or an iPhone.
I don't want to sidetrack the discussion, but if you want to confirm the opensearch description, you can open our site in Firefox, then click the "..." in the browser address bar and then click "Install Andi Search". Or reach out and very happy to talk you through it.
Edit: When I click the address bar, I see an small "A" icon in the bottom row. When I hower over it, it shows "install Andi search".
[Edit: just saw the edit that you found it - thanks again for looking around for it too!]