POTD: Glock 21K?

    I stumbled across this oddity. It is a Glock 21 with an odd looking muzzle brake and an H&K styled vertical grip typically seen on an MP5K. While I have seen some people try to add a vertical grip onto a Glock before, this one is different. It appears there is a screw that is acting as the bar to keep the MP5K grip onto the Glock 21. Does anyone recognize the muzzle brake? In the bottom left corner it mentions a website yourprops.com/user/Matsuo which makes me think that this might not be a real firearm and possibly airsoft.