MULE Tactical unveils AR15 hidden Glock stock

It's a toy. No clear advantage to having it.

You can reload another mag in the time it takes to get the pistol out of the stock. Mags are cheaper and easier to carry/maintain that that thing also.

It will go nowhere. It'll be cool for the urban commando crowd for a while, then the company will go belly up due to lack of continued sales.

"I wouldn't really be that worried about keeping an unloaded weapon secured in the middle o****un battle as bullets are flying in my direction."

Perhaps, but you're overlooking the possibility of having to transition to your pistol, and then transition BACK to your long gun (when neither weapon is dry).

I'm not hating on the product per se, but I bet any trained officer would be considerably faster going back to leather with his/her sidearm and redeploying their long gun from a slung position, rather than having to reinsert the pistol back into that stock and then redeploy the long gun.