Homekit
It is true that the homebridge integration is unofficial and Apple could shut it down.
In June 2017, Apple announced an official integration which is quite similar to Homebridge in that it is software only and said it is now available for hobbyists to connect their own devices to HomeKit. Use by individuals on a small scale is free. So if you want to go with something similar to homebridge that is officially supported by Apple, use that method:
IOS App Alternatives
As far as your other question, I didn’t quite understand it. The best app for controlling SmartThings devices on iOS is the official SmartThings mobile app. That’s the only one that will let you access all SmartThings options.
If you were asking about other third-party apps that might have a smoother UI or some other benefits, There are really only a few right now and they do different things.
- ActionTiles is a very popular third-party dashboard. It works in most browsers, so will work on an iOS device. It let you customize both the look and the devices being shown. But it’s just a dashboard, it lets you toggle devices on and off and shows you status. It doesn’t let you create new rules. People also like it because it let you give a child or a housemate the ability to toggle a specific set of devices without giving them full account access.
- SmartRules is an iOS app that lets you create new rules for SmartThings. It has a very nice graphical interface and also has a “do while” capability which the official SmartThings mobile app does not. So it is also quite popular. (There is another rules engine which is free, webcore, but is much more technically complex and doesn’t have the same kind of graphical interface. Quite a few people use both, using SmartRules for everything it can do and then shifting to webcore if a rule is more complex than SmartRules supports.)
WebCore is essentially a scripting language for SmartThings. Very powerful, but again quite complex. There are many community members who will be glad to help you with it if you get stuck on anything. But it’s not an iOS app, it’s intended to be run on a laptop browser.
- Stringify is another third-party app which is worth looking at. It’s not specific to smartthings but it does have SmartThngs as a supported platform. It’s basically a rules engine that falls in between smartrules and webcore in terms of complexity and power.
So I’m not really sure if I’m answering the question you’re asking about apps, but hopefully this information is of some interest. 