I wish there was a picture. They must have taken a Sig Brace and permanently attached it to a sub 18" shotgun making it over 26". You can do a 14" shotgun with a birdhead grip without going NFA. It's one of those weird loopholes.
The ATF ruled that since it's over 26" it is not an AOW; and since it's not fired from the shoulder it is not a shotgun. The ruled that it is a 'firearm' only and legal. What people fail to realize that individual states have laws with verbiage the mimic the NFA verbiage and it could still be illegal in most states. Is saving a $200 stamp worth it to cut off 4" of barrel and risking a court case to prove it's legal in your state?