Actually this image is a compositing of front and back side PCB into a single image. The GEKO consists of only a single board between the two case shells.
The frontside of the PCB carries only the LCD, patch antenna, and key contact pads. The backside has a comparably low component count, a straightforward design.From a manufacturing point of view, I would consider this as a device with a 50US$ end user price. The main blocks: RF, power supply, controller, flash rom, correlator, RS232 interface, can be easily identified.
The case has a very simple, yet waterproof design. There's a rubber lip around the frame, the contacts of the battery compartment are glued into the case, the LCD window glass is a separate part glued into the front part of the case.
The large shiny box contains the RF parts of the receiver. It is shielded to prevent interference from the digital parts or other gear.
Note the little shiny round button on the back of the pcb, right to the barcode sticker. At first glance, it looks like a coin cell battery - but it is in fact a supercap. Seems Garmin switched from rechargable batteries to supercaps. In current units, all temporary data is stored in flash rom, not battery buffered SRAM. The supercap is only needed to keep the clock running while the receiver is off.
 

This picture is © Carsten Kurz, no unauthorized use. Click  for highres version