BudsGunShop.com - Tax stamp

no it does not require a tax stamp as it is classified as a pistol with a arm brace adding vertical grip or a full stock would make it a SBR (short barrel rifle) and would then require the tax stamp

Larry, no Sir. The Brace in stead of a Stock classifies this as a standard Pistol/Handgun instead of an NFA short barreled rifle SBR.

No, it is considered a handgun and is treated the same way as any other handgun. Putting a stock and/or a vertical foregrip would require a stamp however.