The Galactic Modeler kit is a 3v system that relies on the use of LESs with effects built into them - blinking, strobing, flicker, etc. This translates into having to rely on battery power or installing a voltage regulator to run the system from an outlet. That was a big consideration for me because it simply didn't have the voltage and amperage necessary to add much to the system down the line as the project evolved.
The system relies on the pre-programmed sequences of the LEDs, so if I wanted to build the ship from TMP, I would be in good shape because the lights above and below the hangar entrance are steady-on lights. But, if I wanted to model the -A from ST VI, these would have to be swapped for strobes, which would require me tinkering with calculations of Ohms Law to guarantee the correct resistor value to cover the change.
I wanted an accurate RCS thruster effect from the system, which flickers and fires in a screen accurate sequence instead of remaining on constantly. The GM kit doesn't allow for that feature with re-engineering the components.
I wanted sound. This was a personal choice. While many times, a sound module often comes across as a bit hokey, it seemed wrong to me to see the photon effects without sound. Plus, I wanted enough space on the board to include the sound of Garth Algar ("Wayne's World") whistling the Star Trek theme before admitting, "Sometimes, I wish that I could boldly go where no man has gone before". The GM system is not set up to do any of that for me.
The GM kit uses fiber optics for some of its lighting. For a ship this size, fibers do well on portions of the interior to draw a little more interest, but to my eye, they are underpowered for exterior application in the nav/strobe positions. Great for pinpoints of light, but worthless for trying to get much more. A lighthouse LED used in those same positions is far more convincing in terms of appearance and brightness.
With the 12v system, I have plenty of power to expand on the system and add more LEDs where I need them. All of the effects depend on a digital circuit which is timed out to the movies rather than reliant on the individual LEDs to deliver the effect, so simulating a space dock start-up is a breeze. Not sure if GM can do that.