Focus is probably the best option on iOS but I don't trust Mozilla to block tracking the way I want it done, I'm far more comfortable with uBlock Origin handling it. If I want the extra protection of deleting my cookies and history on exit I'd rather just start a private tab. Most of the time, I want to stay logged in on sites.
Why Focus on iOS? iOS has had a framework for third party content blockers for years. If you install a content blocker for iOS, it also works with other apps depending on which webview they use. For instance they work with Feedly.
For me it's not a matter of trust, it's just that there's no customizability to the ad-blocking on Focus, even at the level of choosing blocklists to subscribe to, or adding particular elements to be blocked.
I don't want a company that releases a "privacy focused browser" with telemetry enabled by default deciding which tracking is "ok" and which isn't. I love Firefox compared to other browsers but there's definitely some user-hostile choices being made at Mozilla and I'd rather they just not get involved in ad blocking (other than ensuring the add-on architecture allows proper blockers to do what they need to get the job done right).
