Hi
I assume you are referring to this page? If you cant see the option for the simpleBGC controller its because its currently out of stock. Buy you can subscribe to stock notifications on the SimpleBGC page
The 3 axis handheld brushless gimbal requires some assembly (included with the gimbal) However it comes arrvies partially assembled, you will just need to do some assembly, and attach the motors. Then you will need to connect up the flight controller and balance your camera, more info on how to do that here
The picture below shows the partial assembly of the gimbal (how it arrives)
Hope that helps 