The AQ50D supports 8 different copter configurations, quad+, quadX, hex+, hexX, Y4, Y6, OctoX and X4. It has a 6DOF IMU, but only flies in ATTI mode, with no option to switch to manual mode, so you won't be doing any aerobatics with this one. It also supports 2 axis camera gimbal stabilisation and the closed source firmware can be upgraded using an additional cable.
So you've read the specifications and I can feel you thinking what's so special about this board? Well, what makes this board so special is that you don't actually need a computer to set it up. It has 4 dip switches which are used to select the copter configuration, quad+, Y6 etc, one calibration button and a gain potentiometer. Once you have done the throttle calibration on all of your ESCs, you connect them to the board, connect up the receiver with the supplied cable, power it up and push and hold the calibration button until the LED flashes, set the gain to about 50% and go an fly.
Now that's what makes this board special! That and the fact that this board seems to be quite immune to frames that produce a lot of vibration and can keep your copter flying really stable in strong winds that would keep other controllers grounded. I've tried a lot of different flight controllers and none of them have come anywhere near as close to this in terms of stability.
You can of course connect this board up to a computer to adjust settings and you will need to do that in order to adjust the gain and servo speed if you're going to use a camera gimbal. In the GUI you can adjust settings for the flight control, but I'd really just suggest sticking with the default settings. The GUI is nice and intuitive to use and has a good layout making it easy to figure out what you're adjusting.
The board does support future updates and add-on sensors, but the developers really seem to be taking their time to come out with firmware updates and hardware upgrades. In the last few weeks we've finally seen the altitude sensor add-on, which will allow altitude hold function and early tests of it are looking promising. Apparently there is a GPS board on its way, but the prototype was first seen over a year ago and no news since then.
Pros: Ease of use, great flight stability, intuitive GUI
Cons: Price, lack of features, slow to release upgrades
Here is a little video showing you just how good this controller is straight out of the box.
For those of you that don't understand French, he basically explains that he has a brand new board that he's never tried before and he then goes through all the steps of calibrating it, once by pushing the calibration button and then the stick calibration which involves holding throttle up and rudder left for a couple of seconds.
Ignore the video title, it's a bit confusing about the name of the board. There are basically 3 versions of this board, AQ50, AQ50-Pro and AQ50D. The latest, AQ50D is the only one worth buying (the one shown in the video) as the other 2 have thermal drift problems which are quite annoying. The AQ50-Pro can be upgraded with an add-on sensor, but avoid this option as its still not as good as the AQ50D.