Apple still doesn’t let you add a custom search engine to Safari, which is one of the reasons I started using Firefox on iOS a few months ago. But xSearch gives you the next best thing. You can add search engines to Safari that are triggered with a command in the address bar.
For example, I setup my SearX instance with “.”. So I can select the address bar, enter a period, space, and then my search term. I still want to see Apple add native support for custom search engines, but I guess I’ll have to settle with this for now.