Homebridge is software that started out life as a Philips hue bridge emulator. It works by using that emulator to fool HomeKit into thinking that other types of devices are hue bulbs. (Seriously, that’s how it works.)
Over the years many different people have contributed different Homebridge “plug-ins“ that are software that convert the messages from other kinds of devices, everything from Ring doorbells to smartthings hubs.
You can run the software on your own device, typically a raspberry pi. Or in the last two years you can buy a hardware device that comes with the basic homebridge software already installed. HOOBS is probably the most popular of these.
It’s important to note that Hoobs is not itself a hub. It can’t talk directly to a Zigbee device or a Z wave device. It’s receiving messages from the smartthings cloud service. Then it’s converting those messages, using the plug-ins, into something that HomeKit will recognize.
Note that many of these integrations are one way: you could, for example, bring devices attached to a smart things hub into the HomeKit app, but you couldn’t bring devices that communicate with HomeKit back into the smartthings app.
So it’s useful for some people, not others, it just depends on what you want to do with it.
HOOBS makes it sounds like it’s as easy to use as the app for consumer devices like ring: it’s not. The plug-ins are pretty technical and they can need some tinkering to get them to work.
Home bridge is definitely an option for some people, but setting it up it’s probably overkill if all you want is reliable home/away indication from an iOS phone/tablet.
Also… right now the smartthings homebridge integration depends on groovy and the smartthings groovy implementation is going away pretty soon. And so far I haven’t heard of anyone who’s volunteered to rewrite it for the new architecture. 
You can talk to people who are using it in the following thread: