GK-2A/ GK-2AH: Differences
The GK-2AH includes a bracket or "harness". The GK controller (the triangle shaped box that contains the controls), mounts to this bracket first, then the bracket can be mounted to the guitar by using the existing rear strap screw.
The GK-2A does not include the bracket, so the controller is mounted directly to the guitar's body by either screws, velcro or double sided tape.
The actual function, size and specifications of both the GK-2A and GK-2AH are the same.