Here is how i use it to control my openHAB bits. I have an IR receiver plugged into my Mac Mini (OH is running on a Pi in a different room). I then register a dummy TV device (note that i don’t have the actual device) with Harmony (pick one with lots of buttons, the Panasonic TC-P65VT30 is a good candidate)
Then using Flirc (the ir receiver) on the Mac I tell it that I am going to record a IR signal and these are the keys I want you to press when you receive that signal
Make them super obscure then you press the button on the remote you want to associate with those keys.
Then, I use Keyboard Maestro (though any custom keyboard shortcut trigger thing will work like BetterTouchTool, Script Events, even the built in Mac system prefs) to do something when those keys are pressed.
(I don’t know if you have a Mac, if not I am sure there are equivalent applications for whatever platform you need)
Keyboard Maestro lets me do anything, I can fire a shell script to send a http request to openHAB, open an Application, send shortcuts specifically to an application.
Once the buttons are in the Harmony Hub I can use openHAB to simulate presses.
E.g I have a “good night” sequence in openHAB that i trigger with HomeKit, it starts to dim the lights downstairs, lights the bedroom and landing, checks to see if the harmony states that an activity is running (and which one) then powers it all off.
I also use the Harmony to control individually the volume levels of Squeezelite and Kodi. Turn on the fan via a remote power switch from the remote.
So whilst the API is a little lacking, you can easily hook several things together.
Yes it might sound like a lot of faffing, and it is, but it works and is very flexible.
I hope my ramblings help somehow 