The 250G is an overdrive based on the DOD 250. The G refers to the grey colour of the first DOD 250 models, as the actual models are painted yellow.
This kit contains all parts you need to build a fully functional effect pedal. You can select the enclsoures you want. You only need a 9V battery or power supply and 2 knobs for the potentiometers and 6.3mm shaft.
Here are 2 sound clips for the 250G: