I‘ve been using Kagi since September as well and I can only recommend giving it a try.
Being able to personalize search rankings is something I definitely wouldn‘t want to miss anymore.
One thing I’d like to mention is that they‘re also really great at listening to feedback. For example, they recently added an indicator for potentially paywalled sites to the search results, because users have suggested it.
Flatpacks are very restrictive by design. While this is a good thing in many cases, it makes it very difficult for tools like EmuDeck to work properly. For example, automatically installing other applications (in this case: emulators) isn‘t easily possible. This would make a flatpak version of Emudeck pretty much useless.
While I understand your concerns, I think installing an AppImage which has been built on Github from open source code just isn‘t all that risky.