Update 1: Moved most of the Xiaomi devices to the new Mijia Multimode Gateway tonight to test for stability over time. So far, it's been a breeze. Everything paired just as fast at they do on the Aqara HomeKit Hub, with the exception of the Opple 6 button controller. That takes slightly less time to pair on the Mijia Multimode gateway. Maybe that has something to do with both devices supporting Zigbee 3.0 
BUT, there's a problem right now for me. I have to keep the Opple 6 button controller paired to the Aqara HomeKit Hub, because for some odd reason, that one device is not exposed to HomeKit when paired to the Mijia Mulimode Gateway, but it is exposed to HomeKit when paired with the Aqara HomeKit Hub. 
This make no sense, and I hope for the sake of those that will buy this Mijia gateway that they will change that soon, because this is a fantastic button controller. One of my favorites. I have also created a simple RM rule that gives you toggle capability in HomeKit, which isn't normally supported for some odd reason.
Other devices I have not moved are an Aqara contact sensor and Mijia contact sensor, because I need them to be joined to the Aqara hub in order to trigger the doorbell sound and the alarm sound. You cannot trigger sounds from one bridge to another from the Mijia Mulitmode Gateway. This is very odd too, since in previous Mijia gateways this was always possible. Maybe it will change in the future, but it's very strange that the first gateway they produce without a speaker, cannot trigger the speaker of another gateway to make up for it. 
I have also not moved a my Mijia motion sensor at my front door. This one I may test later, but for now it will stay paired directly to HE. Where everything has fallen off at one point, this one never does. Maybe for two reasons – ONE: It is a Mijia motion sensor not an Aqara, and they seem to stay paired to HE better for some reason. TWO: It is constantly powered by a 5v adapter with a 5v to 3.3v buck module, and this may be a key factor. This sensor has also received the hack that lets it update every second if you wish. Mine is set to update every 5 seconds. It's been working fine in HE, but when I once tried to pair it to the Aqara HomeKit Hub with the hardware hack in place, it would pair, but the status wouldn't update. Perhaps it will be different with the Mijia Multimode Gateway.. This isn't one I'm going to rush to find out though. It's been so stable in HE, there's nothing but knowledge for me to gain from such a change.
Lastly I have not moved my Aqara Leak Sensors. They are still paired to HE and will stay that way. Why? Because they have never dropped once. The last thing I want to do is experiment with them on the Mijia hub. I'm sure they would be as solid as everything else Xiaomi is on their gateways, but the one under my Kitchen sink just saved me this last Sunday. Worked exactly as it should have. Not broken, so I'm not going to "fix" it.
I'll update this post in a few weeks with how things have been working. So far, everything is just as responsive at the Aqara HomeKit Hub, so except for the missing Opple button controller in HomeKit, it's still a good buy. But for now, if you're interested in using an Opple controller, stick with the Aqara HomeKit Hub (Or maybe the special Mijia Gateway for MiController if it's supported there and shows up in HE).
Update 2:
I'm out for now.
Turns out there is still a beeping. This thing must have been driving early reviewers nuts! It's not that bad now, but it's still annoying. I can understand how it must have seemed so random to the them.
What they did in update 1.4.5_0005 and 1.4.5_0006 was to remove a startup confirmation beep and a successful connection to the internet confirmation beep. What they did not remove was the Zigbee link confirmed beep. The Aqara HomeKit Hub does that, but it speaks it. What they're trying to do I guess, is confirm that the Zigbee network is up. With the Aqara HomeKit Hub, it says "normal link confirmed" every so often, but only when you trigger the first device that you paired to the hub.
The Mijia Multimode Gateway is beeping twice when I pass in front of the same motion sensor that I paired first to it, and it's only happening every so often. I'm almost certain that's what it is. With the Aqara hub, you just turn down the speaker. The alarm and doorbell are local automations, so you just set their volume levels in the automation and then you can turn the hub main volume down so you never hear it. Can't do that with the Mijia's beeper.
Thought about opening it and blocking, or removing the beeper if possible, but the thing looks like it's been welded closed. I don't see any way to open it. Nothing pries away from the sides or bottom. I'm interested in it's potential, so I don't feel like destroying it just yet. I'll wait and see if they come out with an update.
In the meantime I do have an experiment going. I have no idea what they thought was so useful about the link confirm feature, since a light turning on pretty well confirms it. But I got to thinking that maybe it's an Aqara thing for security devices. I have a Mijia motion sensor in the basement and it's the only thing joined to it. I'll test that tomorrow and see it beeps in the same way. If not, then just making sure you use only the Mijia security devices, like the motion sensor and the contact sensor may be necessary. I have both of those to test with. They are sometimes a little more expensive, but they do look nicer than the Aqara in my opinion. devices with it may be the only way to fix that issue. I have a Mijia button, but not an Aqara, so it won't be a conclusive test.
Otherwise, it's a great little gateway for the price, but that beeping isn't tolerable 
, especially when I have the Aqara HomeKit Hub and it's great 
. The Mijia did seem a little faster responding to the motion sensors, so that's something to look forward to with the T1 devices and this gateway, as well as the Aqara M2 still to come.
Update 3: Latest firmware update may have removed the beeping for link confirmation, but I cannot be sure. I also changed the pairing order (e.g. Mijia sensor first, then Aqara sensor) at the same time that I did a firmware update. But I have lost interest in this gateway after discovering that if it does not remain connected to their cloud, it stop communicating with the paired devices, and in fact does not restore the link to the devices. The think drops it's connection to Mijia and Aqara devices alike!
If you don't care about their hub constantly needed to communicate with their server in China so that you can use local HomeKit, then maybe you're fine with one of these. For me, I am absolutely not OK with that. I purposely block the internet connection of my Aqara hub to their servers, and HomeKit together with all the sensors, continue to work. I'm not certain, but I think this Mijia hub may be using the new software based HomeKit authorization, so that would explain why the need the constant internet connection for HomeKit as well as their own automation software. However, that doesn't fully explain why it drops connection to its own devices.
The Aqara HomeKit Hub does for certain have an Apple MFI chip for HomeKit, and it can remain blocked from the internet indefinitely. All the Aqara and Mijia devices will continue to work perfectly.
Mijia Multimode Gateway for HomeKit now receives a DO NOT BUY from me
Aqara HomeKit Hub is excellent and the software is very easy to use and well designed. For Small, inexpensive and good battery life in a sensor, I do recommend the Aqara HomeKit Hub if you're an iOS user and have one of the required always on Apple devices to link HE virtual switches to it via HomeKit automations.
Update 4
I’m sticking with DO NOT BUY from a personal point of view. I’ve heard the Aqara branded T1 cannot join the Mijia Multimode Gateway. However it does appear there is a Gen 2 of Mijia devices on their way, so that may not matter as much. I’ve had no trouble with the Zigbee 1.2 devices from Xiaomi when joined to their gateways, so none of that really matters to me.
The beeping is fixed in the latest firmware update, except for when it reboots or joins a device. Fine by me. What is not fine with me personally is the device must stay connected to the server in China or devices WILL stop responding after a few days.
If none of that matters to you, it’s one heck of a good deal. And for those of you out there that want to join it to MiConnector, there seems to be a way, as long as it isn’t at the latest firmware. Apparently there’s also a way to open it up and short some connections to allow firmware downgrades. Too much trouble in my opinion. Just connect it to HE through HomeKit. Here’s one way to do that without having to be an iOS or Mac user.
Update 5
I'm going to reverse my recommendation. There's still some shortcomings with this device versus the Aqara HomeKit versions, but after a recent firmware update to the Mijia Multimode Gateway v1.4.7.0115, the devices no longer go off-line in HomeKit when you block the gateway's access to the internet. So while their internal automations will stop working (unlike the Aqara HomeKit hub) the Mijia local HomeKit automations keep working (NOTE: As long as it's powered. Does have to reach out to the internet temporarily to reactivate the MFI software authentication when power is lost).
Why should you care? Well the Gateway is $20 and supports up to 64 devices. If you really like the Xiaomi devices, but you've been struggling to keep them joined to HE, I can tell you that they do not drop at all when joined to Aqara and Mijia Gateways. So if you're up for installing HASS.IO (Home Assistant running on HASS OS) in Virtual Box on a spare computer (very simple) or imaging HASS.IO with the HASS OS onto an SD card (also very easy), then this project will take devices added to HA via the build-in HomeKit Controller integration and bring them directly into HE as if they were local devices. No configuration other then to add the IP address of the computer (or virtual machine) running HA and the access token (AKA the Home Assistant Long-Lived Access Tokens).
You won't need to type or know anything in Yaml, no clunky HA automations are needed, no virtual devices, no MQTT brokers. Just set this up and every device you add to the Mijia or Aqara HomeKit compatible gateways will show up in HE as soon as there's a change to the Xiaomi device.
Mijia or Aqara HomeKit gateway > HomeKit Controller on HA > HE import driver
