Home kit is a tricky concept when you get into it. There is no "app" that is available, rather it uses various controls native and deeply embedded into the iOS.
This app helps bridge the gap that Apple has left without a dedicated app.
This app takes the major controls from home kit enabled apps and works to blend them into one. Lighting, thermostat, motion and more are collected and culled into an alphabetical order off the main screen.
Across the bottom is a group of tabs that allow you to set each device as well as group devices by room and zone. You may also set triggers that activate scenes based on time or other events. (I said home kit was a little complicated!)
The goal of the app is to easily allow smart devices that would not easily play with other smart devices a way to see and work as a whole group.
This app achieves this goal and therefore I feel is successful.
What I see missing is a roadmap sharing the next round of new features and a time table of when they will come out, (an app of this price should have one). Also, collecting user feedback in a way that the user knows if a question has been asked or a solution has been provided might take some repetitive answering away from the developer.
As far as some features that a $15 app is missing are the items that the other apps have. At this price, most everything should be available that is available in the devices native app. Here are a couple examples:
This app is missing some "best of breed" options that are native to other smart device apps. When setting a time trigger, the Phillips Hue app allows you to pick the days of the week; this allows an easy way to set a weekday or weekend trigger. Other apps allow a Hue light the option to strobe. These items are missing from the Home app.
Now, this is not a simple app and getting it to talk with all the other early versions of HomeKit enabled device apps is a feat.
This app gets the basics accomplished when it comes to merging various apps together, but in doing so, is lacking is some "over-the-top" controls. As mentioned, at this price point I would expect almost every option for every device to be available.
Now, this app will do everything the smart device apps will do but in a slightly less intuitive manner (in some cases).
It is missing the ability to choose scenes by the day of week. If you want a scene to fire only on Mondays and Fridays, it will be a major effort. If you want the same scene everyday it is easy; but on weekends a different schedule would be nice.
It is the only thing that is out there at the moment so it is the natural leader. Hopefully it will improve and stay the leader.