10" melonite pistol upper

Saw this pistol upper for sale no bcg or charging handle included … Doesn’t know the manufacturer but says it’s melonite … Looks snazzy but of course I’m hesitant … The cap on the end , what purpose does it serve and does anyone have a hint as to who makes this before I drop $350

The cap looking thing looks like a KX3 that is partly under the rail…