Somebody brought this idea to my attention after the unveiling of my foregrip extenders. This item is a special adapter made in the likeness of the extenders, except the purpose of this variant is to flip the foregrip around backwards and project it out the front of the marker, hanging down under the barrel. The pictures show it better than I can speak it...
As with the extenders, this item contains a small circuit board hidden on top of the foregrip. I should also mention that the ones I made (pictured above) were only prototypes so they aren't the prettiest looking. If I made more of these, they'd be more smooth on the bottom.
The purpose of this is simple: it provides an instant "rifle" feel to the marker. Now hold on, this isn't necessarially a bad thing if you're trying to obtain a more mil-sim feel without going for the total mil-sim marker (TM-7 or TM-15 in this case). The horizontal foregrip has the advantage of making it MUCH easier to aim. However, it has the disadvantage of making it very difficult to walk the trigger, and even more difficult to run while firing at the same time.
Regardless of its advantages and disadvantages, it's not my place to question the merits of custom parts that people are looking for. That's why I am here! Whether you like the horizontal adapter or hate it, you have to admit anyone using it has an EXTREMELY unique Invert Mini setup.