I just picked up a Mi Box from my local Walmart. Woohoo, a new toy to distract me from writing a paper. Anyway, just wanted to mention my experience hooking it up to my Harmony Hub.
I had to add the device manually. I entered "Xiaomi" in the manufacturer field (obviously), and "Mi Box" in the model number field. The Harmony automatically recognized it as a Xiaomi Media Player and added it. I must say, using the Harmony remote to control it is fast . I mean no noticeable lag compared to the Mi Box controller, and honestly it may be a millisecond faster. Full disclosure, the Mi Box and Harmony Hub are placed right next to each other.
I had been afraid it wouldn't work so well, and I would have to find a solution using HDMI CEC, but that wasn't necessary. The only thing I'm missing out on by not using the Mi Box remote is voice search, but I don't use that much anyway, plus I can always use my phone for that.
All in all the setup went flawlessly, and I am loving my Mi Box. Sorry, I can't test 4K content, because I don't have a monitor for it, but 1080p everything looks great so far. Let me know if I can answer any questions.
A couple things I'll note that I've seen. The Android TV HBO Now app starts streaming in HD no problem, but a few seconds in and the quality goes down dramatically. Casting the HBO Now app using the Mi Box doesn't have the same issue, the quality stays high.
But my biggest problem so far is Netflix. It starts streaming find, then about 8 seconds into any program I get a "We're having trouble playing this title at the moment". I can't even cast through the Mi Box because it just opens up the native app when I try, and I get the same error. Hopefully this gets fixed soon.Edit: Nothing seems to work to get Netflix working. Clearing app data, uninstall/reinstall, reboot device, sign out/sign in.
Edit 2: Netflix is working just fine now. I'm chalking it up to magic.