The Hobbyking KK 2.1.5 flight controllerYou might like to take a look at my build with the KK2.1.5 here
Turnigy Talon Carbon Fiber Quadcopter Frame build
If you are looking for a serious contender to the KK2, you might want to check this article her
CC3D flight controller
Well i will be the first to admit that when i originally weighed my flight controller purchase options I neglected to look at the KK 2.1.5. My buddy recommended it to me saying it was quite a good controller, but I was looking for GPS, bluetooth, telemetry and plus all the options that megapirates flashed board has to offer and yes i was probably way off due to the fact that this was my first quad build, but don´t get me wrong it has been a fun process learning about how quads work , configuring Bluetooth and getting the GPS to connect, smoking a thing or two, i would do it again, but if you looking for flight time, easy installation, simple no fuck around controller the KK 2.1.5 is for you.
Firstly the price is very attractive 24 bucks off Hobbyking, compared to 70 bucks for a Crius or MultiWii pro, the board comes in a foam casing that you can use to mount the controller with on your multi-rotor to protect it from water and light knocks. I believe that you can for a few bucks more purchase a hard case version.
Secondly there are roughly eight or nine wires that you need to get connected and then you are off, all configuration is done on-board the controller using the LCD screen and this is specially handy to making small adjustments to your multi-rotor between flights.
This board comes with a stabilization or auto-leveling, this can be activated by either flicking an auxillery switch on the radio or using the stick control. Which ever method you choose requires a simple in the menu activation. Auto-level works very nicely on this board, Even though i gradually am learning to navigate a multi-rotor, i still crash with the Crius/MultiWii due to wrong PID settings and so one. They have and still do give me problems setting up. With the K.K i was able to drain several batteries with out a single crash. You can download newer firmware and a well made manual from this guy http://www.rcgroups.com/forums/member.php?u=367321