Trying to cheap out while buying my second flight controller, I was looking at the alternate boards on HobbyKing. They had this blue flight controller...
This board, in particular, has a ATMega 328 on board. And as opposed to what you'll find in a multiwii based setup, three separate gyroscopes. Sadly, there are no accelerometers, so the board has no way of figuring out which direction is down.
The board doesn't support CPPM. It doesn't know what horizon mode it. The board's forward direction can not be changed. It can't be programmed without an ICSP programmer. However, it does allow for some onboard tuning.
There's no button on the board, so "on boot options" are commanded via the transmitter, and the three pots on the board. By swinging a pot to the full left position, you command the board to enter gyro reversing mode.
The board does have a built in arming function, With the throttle at low, you swing the rudder full right, or left, to disarm, or arm. When armed a red light shows on the board.
So what does the board do? You might ask. Well it supports about a dozen mulitcopter configurations, with one to eight motors, some stacked, some not, and some stabilized by servos. It's really quite the resume. But no mater what you fly, it will be in acro mode, all the time. Because the KK doesn't know what way is down.
The default configuration is the "plus" configuration. With one prop leading, as opposed to the usual x configuration most of us are accustomed to flying. The only way to change that setting, is by flashing new firmware on the board.
These boards retail for $12-16. I can't imagine a situation where this board would be preferable to a Flip, or Naze. If you have an unending, burning desire to fly one of these, be sure to pick up a package that also gets you a ICSP programmer. You should also be buying a set of at four servo extensions so you can wire up the receiver to the FCS.
I think the nicest thing about this board, is that the channels are well labeled. Unlike the Flip, KK2, or Naze32.
Sadly, the only lesson to be taken from this, is that quadcopter FCS technology has really advanced. The KK 5.5 is a relic. A cheap relic, but for $4 more, you can get a Flip based board, so the decision isn't a difficult one.