I have the GS shelves and like them a lot. Mine are 18' long (3 - 6' lengths). I have no problems fastening them together. I use a flat blade screwdriver and hold the pin vertical and just tap the screwdriver into the slot a few times. Simple to do. Then I tap the pins on the rail and attach the next piece.
It helps if you have a helper. While I align the pins, my wife taps the next shelf in with a wood block and hammer. I built the walls myself so I know my studs are 16" on centers and the wall is plumb. No need for washers if the wall is straight.
It took us around 2 hours to install all the shelves. I have a section of my layout running around the walls so I had to keep that in mind when I spaced everything out.
Donald