Here's the retail packaging for those not familiar with it:

The games in it aren't the greatest, IMO.
Insides overview:

What is clearly a GOAC in the gun grip in the lower right of the pic. Middle right is the Menacer (which was a large bazooka looking thing orginally) reduced to a tiny board, connected via wires labeled with controller data signals. A small bit more details in the notes of the Flickr image.
GOAC closeup:

Slightly rounded to fit grip, but not very different from other GOAC boards by Radica.
Menacer board closeup:

It's neat that this a separate module, and connects to the controller port it seems. This could mean that you could hook this gun module to a game pad GOAC (modded with cart slot of course), or connect a gamepad to this GOAC.
I need to find out what other games support the Menacer, but I know T2: The Arcade Game for Genesis uses it, which would be awesome to mod this gun to be able to play.