Those WebKit feature flags are developer/experimental settings, so you normally don’t need to change or manually check them at all. I’d leave them at their defaults unless you’re testing a specific web feature. Apple says the default state is how users are generally intended to experience those features.
As for other browsers, it depends on the browser engine they’re using. Most iPhone browsers use WebKit, although Apple now permits alternative browser engines in certain regions and circumstances.
So simply using a different default browser isn’t a reason to change those flags.