Although this gearbox claims to be very modular and customizable, it's anything but such.
The hex shafts you put your slider gears on are a different size than the output shaft, which only gives you the option of putting two gears on the output shaft, instead of any of the gears provided.
There's also no way to have an overdrive (ie smallest gear on output, and a large gear turning it, for speed) because of this fact.